RBW's adventures in tiny Industrial machines. Prazi lathe and milling machine score.

RaisedByWolves

Mangler of grammar, off my meds.
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I have lusted after machine tools since 9th grade shop when I made a working cannon, and much to my shop teachers dismay set off all of the car alarms in the neighborhood with it outside of the shop doors in the faculty parking lot. He thought this was impossible for a kid like me, but I had made other cannons and hadn't blown my fingers off yet. I showed him I could do it, and he gave me an A for the semester.

I always wanted some of the precision made German, Checz or Japanese models, but these were always very expensive and the lower quality ones just didn't do it for me. I had been looking for a benchtop lathe recently as, while I have access to larger machines and in fact have a whole machine shop worth of tools, these small machines fit in well with my hobbies. I liked the Taig lathes, and the Unimat lathe is just so tiny and cute (Fits in a briefcase), but I could just never pull the trigger on one as even used their still $600-700.

Then I ran across an ad on FB market for this Prazi SD300 (Also sold under different names Hobbymat, Shop&Sohn, Prazimat) with the hard to find milling head and called the guy up. He mentioned in passing that there was another smaller lathe included and everything was brand new.

I couldn't get in the truck fast enough.

Thread here.




So some background as to why I'm so stoked about this. This lathe in particular (The whole line really) has intrigued me for much of my adult life. Having read everything I could in model engineering and live steam magazines in the 90s while serving my apprenticeship as a Tool&Die maker I wanted badly to own one knowing how good they were (Vicariously through the writings of others like me), but the $1500 price tag (in 1990 dollars) put them far out of reach.

I had seen them, seen them in use and even got laughed at by my 4th year apprenticeship instructor for wanting to own the CNC version we had at school we never got to use. I later found out he didn't know G code and couldn't operate it, so he scoffed instead. :rolleyes:

These were engineered and in made in east Germany and sold at a loss abroad so they could have access to US dollars as their political and monetary system was crap both before and after the fall of the Berlin wall. The extreme high quality was the only way these would sell and while very expensive for a person to buy, universities, R&D labs and medical manufacturers bought them happily. They are far from a toy like you find in some other mentioned offerings and were much more well made than anything in their class.


So here's what were talking about. This was the day I brought it home along with some assorted tooling I got with it.


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Looking closely you can see the two lathes a Prazi SD300 and an MD200 Miniturn, and the milling head attachment in the upper right.

First lets deal with the lathe.


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Now you're probably thinking "New? that thing is a friggin mess!", and yeah, it was. The pervious owner had it in storage and sprayed it with cosmoline to prevent it from rusting.

IMO he did too good of a job as this **** was a mess to clean off and Ill probably be cleaning and disassembling and cleaning some more to get rid of all of it.

All of that brown, cream and rust colored **** is what I had to remove and its sticky, stinky and nothing will touch it save for copious amounts of acetone. Even then it does not want to come off.

This is what 10min of scrubbing with a stiff plastic brush soaked with acetone, followed with an acetone soaked paper towel removed.




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Its just everywhere and would wad up in little balls where you had to push it around and form a blob to remove it.


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Rinse and repeat until completed.


This is what it looks like today after three days of cleaning, about 4hrs total.


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I have the chuck and cross slide removed, cleaned, oiled and stored for reassembly when I get it into a permanent spot. Once I get it moved Ill reassemble it all, but for now its staying in pieces to make it easier to move.

Under all that crap the surface looks nearly new with only light staining. This is one of the worst stained spots.


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So the first order of business now that its clean enough to work on is removing a broken bolt that held the feed engage lever. This lever allows both power feed and threading via a set of change gears. I wanted to fix it first so I could move the saddle under power to clean the places I couldn't get to and also to generously lubricate everything including the lead screw to further remove any cosmoline residue.


So here's the screw broken off nearly flat. Before drilling and using an easy out on this tiny screw (4MM?) I decided to try and coax it out with a sharpened tap and a hammer.


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What you do is using something harder than the bolt/screw (I like a 10-32 tap) and you grind a fine point on it. Not too fine or it will break off and just chisel away material, but not to blunt or it wont bite. The angle you hold the tap at is critical and you have to constantly go in circular motion, tapping and judging the process as you go.


A little work and it stands proud of the surface and can be grabbed with pliers or even your fingers if its not bound up.


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All fixed up with a new screw in place for now. Ill make some kind of handle for this as one of its first jobs.

You can see the piece of broken screw that was removed laying on the table.

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So for now Ill finish up with a short list of items I want to make or add to the machine to make it more user friendly.


It needs a micrometer carriage stop.

A set of linear scales. The handwheel dials are tiny and not to big around which lends to inaccuracy's in reading and or turning/stopping them to get precise depth of cuts.

A quick change Aloris style tool post. This I may source or if I cant find what suits this machine Ill make it.

A chip tray and back splash are going to be a must.

And finally Ill make a copy of the low speed kit you can buy for these. This kit gives you two lower than stock speeds for threading and tapping or other delicate procedures.
 
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I got the chuck cleaned up today and it turned out to be a really nice little chuck.

When I started in on this it looked more like a glazed donut or a wheel of cheese rather than a piece of tooling.

I had to soak this for two hours in acetone to get it to turn where I didn’t feel like I was forcing it and possibly galling or otherwise ruining the internals.


Here’s what it looked like at that point.




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This must have been what was rusting and made the guy freak out and coat everything in that nasty spray.

It is a cast iron (Mehanite maybe?)chuck so it wants to rust just sitting in a dry room. I tried hitting it with that wire brush sitting next to it but that was going to take way too long.

I disassembled it completely and scrubbed it in the acetone bath and was really surprised at how much swarf was rinsed out.


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That’s mostly iron filings and going through the manual it did mention cleaning “manufacturing residue” out thoroughly before using it.

All the screws and pins were loose so i just chalked this up to the Germans.


Then when I had it all cleaned out and inspected I chucked it up in the lathe and hit it with some fine paper and it came up really nice.

All polished up and ready to go.
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Never heard of the brand and I think the mfg made these. I was impressed to find all of the major parts were serialized during the manufacturing process just like much more expensive chucks. All in all a nice tight little chuck.

I neglected to take pics of the innards as I was trying to do this in between other jobs and forgot.

Many of the “Hobby grade” chucks are a mixed bag of poorly machined scrolls. Rough gears and wobbly jaws. Internal fits and finishes on this one seemed real good, but it needs broken in as it’s a bit stiff. Not crazy about the mounting and I may make a proper back plate for it, but for now it’s OK.


I got the chuck back on the lathe and was pretty stoked about clearing some space and giving the lathe a home.

Chuck looks very nice and works well enough for now. Its a little tight and I may lap the jaws to the body, but I'm going to take a wait and see approach on this. Tighter is more accurate, but its a PITA to have to work (slightly) to open and close this tiny lil thing.

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Now word of caution about lubricating a chuck, whatever you put in the chuck WILL come out of it when its spun up, as evidenced by the spray of oil (Stripe of shame we call it in the trade) on the table, my shirt and pants.

I knew this would happen, but it still caught me off guard when I changed the lathe to a higher speed.:lol_hitti

So here she is in her new home.



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Behind the lathe you can see the ER32 collet nose I plan on fitting, the drill chuck for the tail stock and a couple wrenches. This came with two forged wrenches for maintenance along with some nice quality metric Allen wrenches.


So having it in a home and plugged in I decided to try some things out and began sorting through the boxes I had set aside for this machine. I ran across the tail stock drill chuck and thought I would lock it into the taper and try out the lock of the taper.

On my first try it wouldn't lock, hmmmm, wipe it down and try again.

This time I gave it the good old Tech-school try and Viola, It locked.

And boy did it lock! As you know, lathes and some other tools have what are known as locking tapers. These are shallow angle tapers that when seated properly "Lock" together in a very precise manner as to let them act as one piece, but release when a certain action is preformed.

I played around with the chuck a bit and decided it was pretty nice but needed some cleaning and lube and decided to pop it out of the taper and put it up. Now a strange thing about the tailstock on this lathe, the threads are backwards. :confused:

This means that winding the tailstock handwheel in the normal direction has the opposite effect on the quill than you would expect. This really was the first thing I found on this machine that I felt to be sub-optimal. It just at first seemed unnatural and, well, backwards,:rolleyes: but I figured I would get used to it and everything would be fine.

It wasn't, things went un-fine in a hurry and I was upset with myself for doing something so stupid that I thought I had ruined part of the tailstock.

What I did was try and release the taper, a simple step and that "certain action" I had referenced earlier. Only on this machine as I said, everything is backwards. So in trying to release the taper the internal stop (the end of the screw) came up onto the tang and everything stopped, but the taper did not release.

So figuring it needed some persuading (The handle doesn't have enough mass to whip and make the taper release) I took the plastic handle of a screwdriver and gave the quill handle a little tap and...Nothing. So I gave it a bigger tap and still nothing. So I gave it a harder tap with yet again no result.


Now a tool getting stuck in a locking taper can happen. the remedy for this after all else fails is to disassemble the quill by extending it past the screw threads, remove it and drive the stuck tool out from the back with a drift or a piece of steel rod. So I figured that was the next step.

Only problem was the quill handle was locked up TIGHT! I mean to say it would not budge one bit. This made me despair just a little as I really didn't know what the internals of this quill looked like. I had a general idea, but I of course thought the worst. Picture Rube Goldberg thoughts on the internal workings running through my head.

So I gave up for the night feeling let down and thinking I had to resort to drastic measures to get my self made problem fixed. Im a Tolomaker, Im not supposed to make things worse, only better......FML!

I went to bed but couldn't sleep thinking about this, and about 1AM I remembered something I had read. The quill handle is screwed on and locked with a nut. That means I likely only over tightened the handle and didn't actually break anything.


So I got up and went down to see if I could put this to rest.

Here's the handle arraignment.

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Now before diving in and doing more damage I went over to the other lathe and took the handle apart to see just how it was made. When I got to tinkering with that one I noticed that it turned the correct way rather than opposite every other lathe like the one I had just locked up, It even had a friction micrometer dial!

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So I took it apart and saw how things went together and used that knowledge to get the stuck one un stuck. This is an earlier machine so I just chalked this up to an early design flaw that was worked out by the time the smaller machine was made.

I took the quill, quill screw and handles and swapped them lathe for lathe and now I had a very nice "Correct" tailstock with a micrometer dial to boot!


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Now, knowing what I know, I just take three fingers (Not putting my whole arm into it) and snick the chuck taper into the tailstock quill taper and it locks up nice and comes apart with a little gentile persuasion.

As the British say, done and Done!
 
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So, not being able to leave anything alone I did a thing.

When I was working on this the other day I seemed to remember I had a set of thrust bearings from a 700 size RC helicopter head lying around and wondered if they would fit the tailstock screw shaft. Went and found them and they were a perfect fit......Err, well with some modifications to the tailstock they would be a perfect fit.

I took the bearing carrier that had no bearing in it , (I guess that actually makes it the bearing) and bored it out to accept a 10x20mm bearing that went with the heli head, and also cut clearance for the thrust bearing. You can see the little step going through the threaded hole. And since that threaded hole is the oil hole I also relieved the inner corner of that hole with a carbide burr so oil could flow around the bearing and get to the thrust bearing.




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Here it is with the bearing in place.




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I test fit everything before final assembly to make sure nothing would bind or have any issues and much to my delight it worked very smoothly. Having the other lathe right near by I was able to do a direct comparison and this made a big improvement in the action and feel if the tailstock.

For final assembly I greased the thrust bearing and applied a thin scrim of Loctite 680 retaining compound (Green stuff) to the bearing retainer and assembled everything, then tightened the handle enough to seat and align everything while the retaining compound sets.

Here you can see the bearing and thrust washers/thrust bearing (The greasy looking out of focus lines next to the bearing) on the quill screw shaft.


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Ill leave it like this for 24hrs then put everything back together. I'm really not liking how the tailstock handwheel tightens up using internal threads and a locknut, so I think eventually Ill bore the threads out and install a proper key in the shaft and keyway inside the bore of the handwheel like the big boy lathes have. That way Ill be able to get a more precise setting on the bearing easier than what this current setup allows and Ill be able to apply more force than this setup allows when needed. For now Ill leave it as is until I decide to buy or make new handwheels for the whole machine.


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Very happy for you. Those lathes look to be in pristine condition.

Looking forward to photos and, hopefully, videos of those while in use...

Enjoy the heck out of them!
 
Thanks wachuko! Having a lot of fun with this.:D



I put the tailstock back together and the slides back on. The only problem now is the tailstock action is so silky smooth that the rest of the machine feels like ****. Usually on a big lathe when you need to make large movements on the tailstock quill you "Throw" (spin) the handwheel rather than wind it in whatever direction you want it to go by hand. In stock form the handwheel on this tailstock would make maybe one revolution and come to a stop. Now it will do 3 or 4 and this with much less lateral slop than the stock head stock "bearing".




All done up and ready to use.


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Cant say I'm "Done", but I'm done enough that I can try it out. I got a ****load of miniature tooling for the smaller lathe that I would like to try out on this to see if I like it. Its an interesting little system from the early 70s made by Eddelstaal for Emco for use on the Unimat lathes. Unimats are tiny and so is this tooling.

The tool bits are specially shaped to eliminate 90% of the grinding you would normally do on a conventional square HSS tool bit. This was done for ease of use for the novice market, but also lent its self to production work on larger machines as all you need to do is grind a single angle on the end face of the tool bit and everything else is already done.

The tool bit is only about 1/8" tall and 3/16" wide. The tool holder shank is only 5/16""


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The red paint on this bit designates it as the higher quality of M42 HSS. I counted 30pcs of regular HSS, two of these special HSS bits and 18 of the solid carbide.




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Since I had things fairly in order at this point, I made my first chips!



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Being used to much larger machines I didnt know what to expect from this and Im happy to say I was pleasantly surprised with how well it took a fairly heavy cut. I got some O-1 drill rod for a project and being fairly tough I thought this would be a good test for not only the lathe but also for the Edelstaal tooling.

It worked great, here's a .040 deep (.080 total) cut in a .375 bar at 600RPMs.





Yeah, thats a ****load of stickout, but with everything being new and tight it handled it fine.

So being happy with how well it cut I went ahead and installed some accessories I got with this. In stock form you need to lock/undo
the tail stock and tailstock quill with a wrench. Not the most convenient thing. I got a kit with replacement screws and handles that you need to align, mark, drill and assemble.

So I broke out the instructions and went over them carefully, I never do this but today I did. Since there is no way of knowing where the tap started the hole at the factory, you have to install the new bolt, tighten things down and mark which flat on the bolt you need to drill to have the handle in the right location.


Did that and center drilled the holes.


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I then drilled the holes.

I made this little vise at work when we were slow just for use on small machines. Aint it cute? 1-7/8" wide with a 2" opening and build in parallels and V notches in both vertical and horizontal orientations. Square all round to .0002 and will be happy in any orientation.


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Damn, that chuck is ugly.


After drilling the first hole I didn't like the fit. They tell you to use a #12 drill, but for the second one I used a #13 for a better fit.


Then I used some loctite 680 retaining compound on both and fit the handles.



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The smaller one for the quill was a lousy fit, so I drilled it for the little roll pin they give you and inserted that. The longer one I used the #13 drill on was a nice drive fit with a hammer. It got some loctite too as I'm a belt and suspenders kind of guy.


After letting the loctite cure I installed the quill lock and it worked great, then I went to install the tailstock lock and.....




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Oops! The instructions weren't very clear about this. Never readin instructions again.


Not a big deal really as I have to install a tiny roll pin in the side of the tailstock body to keep this lever from dropping out of site when its released so the tailstock has to come off anyway. They give you a tiny 1/32" roll pin for this but it just looks like it will get bent so Ill probably got with an 1/8" instead.
 
Took the endplate off of the lathe to remove the tailstock to install the lock handle and drill the hole for the split pin.



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I also discovered why the handwheel was bleeding the nasty brown goo everywhere, it was packed with communist grease.

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I removed most of that as it wasn't anywhere near anything that needed that much grease.

I settled on a spot for the split pin and spotted and drilled it and insertd the pin.

Heres the pin they give you vs the one I installed. That little thing was bound to get bent and cause me to have to redo this so I just went with something more suitable. The short little pin was meant for the tailstock handle, but as mentioned it was not needed. The one I went with was right around .100 dia.





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Looks and works good. Hits the handle right about in the middle.


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With the handle either locked or released its out of the way of the tailstock hand wheel and quill lock. Im thinking Im going to make some knurled aluminum ends for these handles to make them a little longer and easier to use.


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All done.




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Having sorted out the tailstock and using the machine a bit I discovered some areas that needed attention. The tool post was an issue because as made it hangs over the end of the cross slide, and has entirely too much leverage on the compound and cross slide ways. This causes it to dip and the tool to bite which kept frigging up the tool height. This was compounded by the tool holder needing to be above its highest setting for the tooling I'm using.


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The adjuster nob sat .030 above the tool post and I really didn't like the arraignment at all as it was kinda wobbly and did not repeat or even stay put. First thing I did was make up a washer to let the toolholder adjuster sit on something ensuring repeatable, stable tool height.

Oof, that's a big drill for this machine.


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Having that done helped, but I still wanted to get rid of the overhang on the compound so I took out one of the toolpost bolts and moved it back. This puts the tool holder over the compound and cross slide ways and puts the force of the cut downwards into them rather than torqueing then downwards and to the left.

So we went from this:


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To this, much better. It almost rests on the compound, which would be awesome, but there is daylight under there.




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This not only gave me much more rigidity, but now I can angle the toolpost any way I want and the lack of one bolt holding it in place was of no detriment.



Before trying this new arraignment out I decided to have a look at the gib adjustment screws as they were quite awful. These were breaking just trying to adjust them which really does not take much force and they also stuck out too far and would hit the compound mounting screws.




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I found some suitable replacements and installed those and adjusted the gibs.



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Looking at the above pic you can see how crappy those gib screws look, and I think they were made out of some crappy leftover stainless or something. Just soft and brittle crap really.


These sit about .100" lower and work much better.



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Having sorted that out, I started in on my first? real project on this lathe last night and made some handle ends for the tailstock quill lock and travel stop levers.

Chucked up an old brass punch I had laying around and came up with a rough idea of what I wanted them to look like, pretty straight forward, just a hole for the shaft, a taper leading to the shaft and since I don't have a tiny knurl I made a tiny parting tool out of one of the Edelstaal bits and cut some shallow grooves.

Kind of hard to see the toolbit tip in this pic as it wants to blend in with the chuck jaw. The tip of the toolbit was only .030 and much to my surprise it parted off the part when finished without any issue.



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Im really getting to like this little tooling system and I kind of wish they were still in production. Then again, with the amount of tool bits I got with this deal and the prices they go for on E bay I might be able to retire if I sold them all off.



So having parted this handle off I flipped it around and beveled the edges with a file and added some detail with a 3/8" ball mill.

I think it turned out nice, but now comes the hard part, duplicating it for the other handle.



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I really need to upgrade the tool post on this lathe as the one that came with it and the holders make it tedious to change setups. I have an OXA tool post coming from chiner which should remedy this.


Here they are mocked up on their respective handles. I need to polish them and clearcoat before doing the final install.

Now I need to make the rest of the handles match. I plan on remaking the handles for the handwheels with tips to match these, but made so they rotate. I think that will give the machine a much nicer feel.


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Got a little more time on the machine and decided the feed clutch wasn't as responsive as I would like it to be. Its a simple dog type clutch but it only has two engagement points per revolution making you have to wait for things to line up properly before engagement. For normal threading this would be ok as the lead screw spins faster, but for longitudinal feed while cutting it sucked.

Looking it over I realized I could cut a slot 90* to the factory one giving 4 engagement positions per revolution.

So I began disassembling it. I didn't think to take many pictures of the disassembly as it seemed straight forward, right up until I got to this little devil clip. These are very tough spring clips and the commies must love them as there used throughout this end of the machine. This one was recessed in under the lip of the dog clutch and was a real ***** to get out. I had to get a jewelers screw driver between it and the inside edge of the clutch dog and work it out of the groove, then wiggle it out further with another screwdriver......All while everything is trying to rotate away from every force I applied.

Took the better part of a half hour, where as a proper c clip would have taken seconds.


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Here's the two I had to deal with. The big one was TOUGH to get off as were the two keys. The little key was not bad but the big one seemed welded in and I had to use heat to get it to come out.



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Next I made a jig to hold it as there really is nothing to grab onto. I thought about putting it in from the back of a C5 collet, but it wouldn't stick out far enough due to that flange. I have no idea what the flange is for but I didn't want to turn it off, so I made a jig.

Here you can see the jig and both halves of the dog clutch.


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All set up ready for milling.


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This piece is a wear part so it was pretty hard and I had to take light cuts, but it went well.

Done.



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I chamfered the square edges to help with engagement a bit and was very happy with the end result. You can see I didn't mill down to the same depth as factory to keep as much strength as possible plus I had that hold down strap to think about, but the drive dog goes in fully.


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When going back together the large key gave me some trouble. This one is what drives the sliding half of the drive dog so it has to be a very tight slip fit and things get a little nicked removing it, so I blued it and looked for high spots and removed them with a file. You can see where that fat snap ring goes in this pic.

Did I mention these things really suck? I would have replaced it with a snap ring, but the groove is rounded on the bottom so I just reinstalled it hoping I never have to deal with it again.



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I had to stop at this point as I need to make a better feed handle, as the plain screw and plastic handle I have in there now feels cheap and I'm afraid its going to break and cause me to crash the machine if it does.
 
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That's a great thread, Wolves. When I started reading it, I didn't want a little lathe. Halfway through, your enthusiasm got me, and I did want a little lathe. Then seeing everything you had to do, I didn't want a little lathe. Now, when you're finished fixing up, I want to buy it.
 
That's a great thread, Wolves. When I started reading it, I didn't want a little lathe. Halfway through, your enthusiasm got me, and I did want a little lathe. Then seeing everything you had to do, I didn't want a little lathe. Now, when you're finished fixing up, I want to buy it.
I’m having a blast with this thing and I’m nowhere near done.

I didn’t really want a mini lathe in the beginning until I found this for sale and looked them up. Back in the day I wanted this or an Emco 5 but the price on entry was too high, and over the years I forgot about them and built out my big shop.

My suggestion is if you can find one, buy it. I wouldn’t be spending this much time on it if it wasn’t worth it. Their pretty good out of the box, they just lack the big lathe features I’m adding on, a personal thing.

I’m way ahead from what I’ve posted so far. It’s either take pics and post or get things done.

I’m also building and outfitting a small mill that goes with this lathe. That is currently eating up all my play money, spent $500 on a T-DRO setup for that so it’s a good thing I can work on the lathe for cheap.

More tonight.
 
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