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9 x 20 half nut problem

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savarin

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Made new rubber wipers that have the added bonus of holding a bit of the oil back in where it should be.
Eagerly awaiting the new half nuts being sent to me from hman along with a couple of other bits. How awesome and amazing is that.
That beats waiting for 16 weeks and probably longer considering the Chinese new year will be upon us by the time they got round to sending the order.
 

savarin

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Whilst waiting for the half nuts I've decided to extend the cross slide screw for a bit more travel, add real bearings to the shaft, make it M10x1 to make the travel calcs easier. The original M8x1.25 thread is very worn in the middle with a lot of backlash but very firm at each end of its travel so it does need replacing.
What would be the best material to use for a new lead screw here?
I have a heap of stainless rod I could use, would this wear ok do you think?
And would brass be ok for the nut?
I have a bit of scrap from a marine pump that I think is bronze of some type, maybe I should cast a chunk for the nut from that if brass is too soft.
Made a start on the new larger handle from a zinc alloy ingot and on the vernier ring and dial from a small length of 60mm dia leaded steel from somewhere (I think it was a drop I was given)
 

savarin

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Once you start fettling you just cant stop.
I have a length of alloy 60 x 100 mm long so that will be the bracket, the handle I've turned from a zinc alloy ingot.
I made a 100 segment circle scale held in the end of the spindle as an indexing aid to scribe the 0.01mm divisions.
cross-slide-1.jpg

The saddle stop is clamped with a "G" clamp so the divisions are all the same length.
cross-slide-2.jpg

Once I finished the divisions I knurled the end,
cross-slide-3.jpg

then bored the middle out with a hole saw then parted it off.
cross-slide-4.jpg

the finished dial sans numbers sitting on the handle with a very smooth fit.
cross-slide-5.jpg

The bearing on top will be in the extended bracket.
I know this flexi lathe cant hold this kind of accuracy but I though with the 1mm thread and 100 divisions on the lead screw it will make the length calculations easier (I hope).
I'm still uncertain what material to use for the lead screw.
I have enough stainless I could use but am unsure if it will wear ok.
The nut will be either brass or some cast bronze if I melt it.
 

savarin

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There are times when I hate turning, reducing the centre of the extension support bracket could only go one pass at a time due to this.
cross-slide-6.jpg


Any way the parts from John Herrmann (hman) have arrived so its geterbackproper.
I took a lot of care getting everything adjusted to as spot on as I could and ensuring the half nuts closed from both sides equally took a bit of fiddling but we got there.
Next I added the brass brush John sent, so simple, so effective, I love it

cross-slide-67.jpg


and with the cross slide shield I think swarf will find it very difficult getting in there.

cross-slide-8.jpg


with the half nuts replaced the old ones are virtually smooth on one side and the other one has half the width of the thread worn away.
I really hope all the care I took ensuring they clamp up equally will prevent this from happening again.

old-half-nuts.jpg


Does it all work now?
Yep
single point M8 x 1 in stainless.
These are for the bearing clamps on the binocular.

cross-slide-9.jpg
 

savarin

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Started on the cross slide shaft but its a long process turning that down from 16mm to 10mm.
However, like all my projects I've been side tracked again.
I'm attempting to make a vernier scale, no real reason in this instance just to see if I can.
The idea is to add a vernier scale to the cross slide dial of my lathe.
On a flexi 9x20 its a bit of nonsense but what the hell.
I have engraved 100 divisions around the dial using a scale I printed off from this site.
http://www.cgtk.co.uk/metalwork/reference/divider as you can see above.
This hopefully will give me an advance of 1/100 of a mm of cross slide travel per division so with the vernier theoretically it should advance 1/1000
I'm thinking if I print off a scale with 90 divisions to the same diameter size as the 100 scale and use that to engrave another dial but just use 20 divisions this should give me 9 divisions in the space of 10 divisions on the original scale.
A quick test by printing both scales and overlaying them to see through the 90 to the 100 underneath seems to bear this out as with the zero on each scale in alignment the 9th division of the 90 scale sits on the 10 mark on the hundred scale.
or should it be a 110 scale where the number 10 sits on the 9 of the hundred scale.
Which one would be the correct version?
Am I on the right track here or just blowing bubbles?
 

Bob Korves

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Am I on the right track here or just blowing bubbles?
Resolution and accuracy are two different concepts. Increasing resolution does not necessarily increase accuracy. On your smaller Chinese lathe, I hope it will make you feel better... ;)
 

savarin

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I eventually used the 110 segment scale, it gives 10 divisions in the space of 9 divisions on the main dial.
Heres all the parts
cross-slide-10.jpg

Assembled
cross-slide-11.jpg

Its a nice smooth action with the two bearings.
I'm really happy with the M10 x 1 mm thread, the longest I've cut and very smooth
cross-slide-13.jpg

Now I have to mill off the excess aluminium from the extension bracket and I haven't worked out how yet.
cross-slide-12.jpg

If you look closely you can see the brass shim where I over bored the bearing recess.
 

BROCKWOOD

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Looking good! I like the way you are tightening your specs & correcting your dial. Mine shows 80 divisions for 0.010 of movement per revolution. Gonna follow your lead on this!
 

hman

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Now I have to mill off the excess aluminium from the extension bracket and I haven't worked out how yet.
View attachment 281568
Consider this ... There's really no need to continue the dovetail profile on the part. It has no guiding or alignment function. I think all you really need to do is clear the slide. So you might consider cutting on something like the yellow outline illustrated below.

cross-slide-12.jpg
 

savarin

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Definitely the way John, thanks.
Still working on a holding method.
 

savarin

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Started milling the waste material with an end mill but it was very rough finish.
cross-slide-14.jpg

So I ground a broken tap to a small raked flat tip cutter and used a small boring bar to remove the rest.
cross-slide-15.jpg

Now its being filed down for the final fit.
Meanwhile -
can anyone see a reason as to why I cannot cut a channel or drill a hole for the extended cross slide lead screw at the end of the cross slide so the nut can travel a bit further?
Would a channel weaken the saddle too much?
saddle-1.jpg

As its in bits to do all this plus replacing the headstock bearings I thought why not go here as well.
If I was designing this I would have placed a roller bearing there for the end of the lead screw but thats probably a bit of overkill.
 

savarin

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I decided I needed a key for the handle so thought a woodruff type would be the easiest to make.
I ground a thin cutter and fixed it into a boring bar.
The bar was held in the chuck and the shaft I wanted to keyway cut was held in a wedge type QCTP holder.
I set the height so the cutter was centered on the shaft and just kissing it.
Locked the saddle and cross slide.
Then the cringe bit.
Gently loosened the holder and adjusted its height so the cutter started cutting, gently tightened the holder which had the propensity to raise the shaft parallel again and cut a little more. Repeat untill the slot is deep enough.
keyway.jpg

Not a brilliant photo but hopefully you can get the drift.
 

Downunder Bob

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G'day Charles, I'm still constantly amazed at the new ways you can create to do the impossible with next to nothing. Your continued use of excessive overhang to get good results is mind boggling as always.

Carry on you've got me beat. I look forward to the day when I'm next in Qld, and I can see some of your toys.
 

savarin

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as you can see there is a brass shim under the holding screws.
The test bar didnt use the shim and a too heavy a cut actually spit the shaft out of the holder making a neat row of divots along its length.
The cutter touched, gripped and levered the shaft out one rotation at a time.
All good fun.
 

jcp

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"The test bar didnt use the shim and a too heavy a cut actually spit the shaft out of the holder making a neat row of divots along its length.
The cutter touched, gripped and levered the shaft out one rotation at a time."

Saw this happen in the shop where I worked. Operator was cutting key seats in a 2 7/16ths x 12' shaft. Machine was a Summit universal mill with a 10 x 54 table set up in horizontal arrangement. Hold down clamping was inadequate and pulled the shaft into the cutter. Amazingly the cutter didn't break. Pulled the entire length of shaft past the cutter. It did trash the cutter mandrel.
 

savarin

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Cut the keyway in the handle by grinding a carbide (horrible) small boring tool thinner and used the saddle handle to gently cut away the slot.
I used the same process of lowering the tool holder after every pass.
handle-keyway.jpg

To stop the chuck rotating I locked it with my indexing system.
handle-keyway2.jpg

I have got to get my act together and clean, polish and blue all my made tools in a forlorn attempt at beating the humidity rust bug.
 

BROCKWOOD

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Here in Louisiana, humidity is a given. Yet with a gas fueled water heater for the house actually located in the garage where I do my machining, no worries of rust at all. I also periodically spray WD on bare surfaces & run a small electric heater while working. Your project is looking good!
 

Downunder Bob

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Cut the keyway in the handle by grinding a carbide (horrible) small boring tool thinner and used the saddle handle to gently cut away the slot.
I used the same process of lowering the tool holder after every pass.
View attachment 282665
To stop the chuck rotating I locked it with my indexing system.
View attachment 282666
I have got to get my act together and clean, polish and blue all my made tools in a forlorn attempt at beating the humidity rust bug.
Charles, have you tried Inox MX3 will stop the rust.
 

Downunder Bob

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Which one Bob? I've just looked on line and there are a variety of Inox MX3 products.

It's called Inox MX3 lubricant, and comes in different container sizes so suit yourself, a spray can is convenient but expensive, a small hand squirt bottle, a 5l container and bigger, you don't need the FG grade unless your working on food machinery.

All the other products like MX2, MX4, MX5 etc are for a variety of uses they are pretty self explanatory on the website. The little hand squirt bottle is a convenient way to try it. Ive been using the 5L bottle now for some time and have a few small squirt bottles around the shop. I use it for protecting metal that is stored outside, especially freshly cut, and or welded. I even give a light spray onto a new roll of MIG wire when I fit it into machine.

Also all my hand tools, also use it as a cutting fluid on lathe, drill press and band saw. It's very good on difficult metals like SS and Al, I don't have a corrosion problem even though shop has evap air con.
 

savarin

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Todays job was making a new cross slide nut from some brass sponge as a test. I will eventually do this in bronze and hopefully solid metal not a spongy mess.
Chopped a chunk from some failed casting and faced it off.
cs-nut-1.jpg

Flipped it and faced again
cs-nut-2.jpg

I kept it as large as I could just in case.
then turned the fixing spigot.
cs-nut-3.jpg

Drilled and tapped then filed to fit the gap in the saddle casting
cs-nut-4.jpg

With such a long thread it is very smooth and not much side play.
I need to add a couple of shims on the top of the boss as if I tighten the fixing screw very tight the movement becomes stiffer.
cross-slide-16.jpg

All bolted up and a nice smooth movement with extended travel both fore and aft.
When the M10x1 die arrives I will cut the shaft 12 mm shorter and use two M10x1 locknuts to fix the handle.
Compared to the original its now joy to use.
 

Downunder Bob

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Waste not want not, still as creative as ever.
 
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