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jpfabricator

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#1
A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.
Img_1921.jpg


I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.
Img_7597_zpscb8b5dd7.jpg


Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544
 
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Bob Korves

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#2
A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.
Img_1921.jpg


I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.
Img_7597_zpscb8b5dd7.jpg


Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544
 

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jlsmithseven

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#3
i like the cross slide a LOT better. but to each his own for sure. i completely agree with that. gotta do it the way it works.
 

stupoty

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#4
I use a threading stop to allow quick retract and reset of cross slide and use the compound to feed in. Before using the cross slide stop it was always a much slower process and easier to accidentally wind back in a few to many thousandths and take a cut that was a bit deeper than i should have.

Sturt
 

higgite

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#5
Congrats on your success. How about a pic of your setup when you use the compound to advance the tool? Just curious as to what your problem could have been.

BTW, I see a tapatalk red X instead of a pic in your OP, but the link to the photo worked fine.

Tom
 

Charles Spencer

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#6
The picture:

20170304_192539.jpg
 

jpfabricator

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#8
When I use the compound the threads look like they aren't timed correctly. It's set at 30*, the tool is sharp, and I'm engaging on the same # on the thread counter. It just looks "off".
When I get more time in the shop I will post some pictures of the fails.

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Tozguy

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#9
jp, to my mind it is worth getting both methods sorted so you can readily use either depending on the circumstances. Looking forward to seeing your pictures.
 

Bob Korves

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#10
First, you want the angle to be less than 30 degrees, never more. And that angle is measured from the cross slide direction, not from the spindle axis. Sometimes the degree markings on lathes for the compound angle are laid out measuring from the spindle axis at zero to the cross slide at 90 degrees, which will give you a 60 degree angle to the cross slide if you set it at 30 degrees on the dial. Get the compound pointed directly in line with the cross slide. That should be 0 degrees, not 90. Then swing the compound to the left as you count off the degrees until you get to less than 30 degrees. Anywhere around 29 degrees is probably fine, it is not critical unless it is more than 30 degrees which will leave a stair step finish on the right flank of the thread.
 

Technical Ted

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#11
I agree with those that suggest you try to figure out why you got poor results using the compound. I've done a fair amount of both internal and external single pointing and I don't ever remember using the cross-feed; I always use the compound set at ~29 degrees. Typically, you will get better chip control because you're cutting with the leading edge instead of both edges. But, whatever way you want to do it is fine as long as you get the results you're looking for.

Ted
 

jpfabricator

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#12
20170304_192511.jpg
This is what I was getting before, same tool, same everything, different advance.
It's like its not threading, but wiping the threads off a little more with each pass.

Sent from my SM-S320VL using Tapatalk
 

neilking

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#13
I had some success with just using the cross slide, but after reading about using the compound I've had success that way too. 20170306_184645.jpg

Sent from my SM-G920P using Tapatalk
 

tweinke

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#14
View attachment 228076
This is what I was getting before, same tool, same everything, different advance.
It's like its not threading, but wiping the threads off a little more with each pass.

Sent from my SM-S320VL using Tapatalk
I have had the same result with the compound set at 30 or so but feeding in with the compound is ok. now I am wondering if I should measure the angle and be sure it is actualy between 29 and 30
 

willthedancer

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#16
I have some thoughts, questions, and a suggestion.

Metric or USS?
I don't know zip about metric lathes.

If USS, how many threads per inch, and what is the pitch of your leadscrew?

What number(s) did you hit on your chasing dial?

My suggestion is to get a 1" - 8 nut from the hardware store. Set up and thread a 1 inch bar 8 threads. Set your compound to 29 and a half degrees off the face of the chuck. Be very diligent about getting the cross slide back to your zero every time.

Sent from my Moto G Play using Tapatalk
 

darkzero

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#17
This is what I was getting before, same tool, same everything, different advance.
It's like its not threading, but wiping the threads off a little more with each pass.

Sent from my SM-S320VL using Tapatalk
This sounds like you were not set to 29deg for threading which must be 29deg off the X axis when using the compound.

Do you have an Asian import lathe? Most hobby size Asian import lathes smaller than 14x do not have a full protractor scale for the compound slide. On lathes like this if you set it 29deg on the scale, it is 29deg off the Z axis and will cause the thread issues you described when trying to thread using the compound slide.

Take a look at the photos I posted in post # 4 here: http://www.hobby-machinist.com/threads/pm-1236-tool-post-issues.28428/#post-248506
 

Tozguy

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#18
I have had the same result with the compound set at 30 or so but feeding in with the compound is ok. now I am wondering if I should measure the angle and be sure it is actualy between 29 and 30
The 29.5 deg setting is recommended to allow for some potential error in the protractor on the lathe, since it is OK to be under 30 deg but never over. I think that it is a good idea to check the accuracy of your protractor for your own edification.

Also, if your protractor is set up like the one shown in the link that darkzero provided, I recommend that you establish a second index mark on the side of the cross slide. Set your compound at exactly 90 deg to the spindle axis and then scribe a mark on the cross slide opposite the 0 on the lathe's protractor. That way you will have a better time using the protractor for threading.
 

ddickey

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#19
Arn't you supposed to feed in with the cross slide the final couple thou? This is what I learned on Tom's Techniques site.
 

Tozguy

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#20
There are so many different threading jobs that I prefer to use the technique or combination of them that best suits the job and equipment as opposed to having the same hard and fast rules to follow for everything.
 

Bob Korves

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#21
The 29.5 deg setting is recommended to allow for some potential error in the protractor on the lathe, since it is OK to be under 30 deg but never over. I think that it is a good idea to check the accuracy of your protractor for your own edification.

Also, if your protractor is set up like the one shown in the link that darkzero provided, I recommend that you establish a second index mark on the side of the cross slide. Set your compound at exactly 90 deg to the spindle axis and then scribe a mark on the cross slide opposite the 0 on the lathe's protractor. That way you will have a better time using the protractor for threading.
On most lathes owned by mere mortal hobby machinists, the compound degree scale cannot be expected to be accurate to within 1/2 degree. Either check that angle more accurately using a different method or simply choose a smaller number than the 29.5 degrees council of perfection, like 28 degrees or even less. Make sure it is less than 30 degrees in reality. Even zero degrees works...
 

ewkearns

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#22
There is a LOT of tearing (rather than clean cutting) in creating these threads. Make sure of your cutter height setting and tool geometry. Consider your cutting oil. Feeding in with the compound is recommended only for threading hot rolled steel and then using a cutter specifically ground for the task. Feeding in with the compound is specifically NOT recommended for carbide threading tools....
 

darkzero

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#23
Feeding in with the compound is recommended only for threading hot rolled steel and then using a cutter specifically ground for the task...

Feeding in with the compound is specifically NOT recommended for carbide threading tools....
That's interesting, I never heard that before. I don't agree but could you elaborate, I'm curious as to why?
 

ewkearns

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#24
When I was learning machine shop, I was taught, in part, by a bunch of guys that were making chips as early as just before the turn of the century. In their day, the material of choice was hot rolled steel and it WAS STRINGY. The technique was developed to grind the threading tool such that it cut on the leading edge only and sent the chip out of and away from the generated thread.... hence the use of the compound rest and the sainted and inviolable 29.5° setting. They were highly amused that the technique was applied to everything, rather than the task that it was specifically adapted to serve... They simply never used the compound to thread anything that would generate a non-destructive chip. (And, today, neither do I.)

When carbide tools came into wide acceptance, we found that the tips of those tools would fail using the compound rest. The carbide was simply not ground to accept a side load. So, abandoning the notion of the sanctity of the compound rest, threading was accomplished using the crossfeed, only, and the problem went away.

I realize that my position is anathema on this matter, but I was taught as much WHY as HOW and it has served me well. I believe that threading using the compound is so sacred, today, simply because it got a LOT more "press coverage."


My 2¢
 

Tozguy

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#25
When I was learning machine shop, I was taught, in part, by a bunch of guys that were making chips as early as just before the turn of the century.
When carbide tools came into wide acceptance, we found that the tips of those tools would fail using the compound rest. The carbide was simply not ground to accept a side load. So, abandoning the notion of the sanctity of the compound rest, threading was accomplished using the crossfeed, only, and the problem went away.


My 2¢
It seems to me that nowadays there is a carbide insert for just about any job imaginable.
 
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Bob Korves

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#26
When I was learning machine shop, I was taught, in part, by a bunch of guys that were making chips as early as just before the turn of the century. In their day, the material of choice was hot rolled steel and it WAS STRINGY. The technique was developed to grind the threading tool such that it cut on the leading edge only and sent the chip out of and away from the generated thread.... hence the use of the compound rest and the sainted and inviolable 29.5° setting. They were highly amused that the technique was applied to everything, rather than the task that it was specifically adapted to serve... They simply never used the compound to thread anything that would generate a non-destructive chip. (And, today, neither do I.)

When carbide tools came into wide acceptance, we found that the tips of those tools would fail using the compound rest. The carbide was simply not ground to accept a side load. So, abandoning the notion of the sanctity of the compound rest, threading was accomplished using the crossfeed, only, and the problem went away.

I realize that my position is anathema on this matter, but I was taught as much WHY as HOW and it has served me well. I believe that threading using the compound is so sacred, today, simply because it got a LOT more "press coverage."


My 2¢
Another reason I prefer the cross slide method of threading most of the time is that the depth of cut dialed in is the depth of cut achieved, no calculating or trig involved, just read the dial and check the thread when you get close.
 

Dave Paine

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#27
I know how I made my first mistake when trying to use the compound set to the 29.5 deg angle. I read the scale on the compound and overlooked the axis which was the reference for the angle. I expect I am not the only person falling for this mistake. My Grizzly lathe made it easier to fall into this trap.

In this picture I have moved the compound to have the scribe mark at the 30 deg mark. On my G9249 lathe, the only number shown is 0 (zero). The marks go up to 55 deg either side of 0.

Grizzly_compound_scale_7615.jpg

After making some bad threads I also changed to using the carriage. I later realised my mistake was setting the angle to the wrong 30 deg, as in 30 deg from parallel to the lathe bed. It needed to be 30 deg from perpendicular to the lathe bed, or the face of the chuck. Easy mistake for a woodworker just starting out on a metal lathe.

I have a decent mitre gauge for the table saw so I cut a block of wood to 29.5 deg.
Angle_block_to_set_threading_angle_7616.jpg

I glued a small magnet into the wood so it holds to the side of the compound.

Wood_angle_block_7617.jpg

I do not understand why Grizzly did not have the scale going to 60 deg. My lathe needs an angle block in order to set angles less than 35 deg (or 55 deg) depending on how the angle is defined.

Grizzly_compound_thread_angle_off_scale_7618.jpg

Interesting post earlier discussing the potential origin of 29.5 deg angle. It is easier to use the carriage.
 

Bob Korves

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#28
(snip)After making some bad threads I also changed to using the carriage. I later realised my mistake was setting the angle to the wrong 30 deg, as in 30 deg from parallel to the lathe bed. It needed to be 30 deg from perpendicular to the lathe bed, or the face of the chuck. Easy mistake for a woodworker just starting out on a metal lathe.(snip)
Bingo! Thanks, Dave. You and MANY others have made the same mistake, and a very easy to make mistake, I might add. Thanks for putting up photos to help explain the problem and the solution. Everyone, please do not trust those compound scale quadrants on lathes to be accurate or to show the quadrants in the orientation that you expect. Stand back, get the big picture, and make sure that you are seeing something that looks like the angle of the block of wood Dave has posted. If you are too lazy to measure the actual angle of the compound accurately, then set the angle to somewhat less than 29.5 degrees, to make damn sure that you are not at more than 30 degrees in reality. 25 degrees will give you no visible difference in your threads, in fact they will probably look better, and even zero degrees will work just fine...
 

Tozguy

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#29
Dave, the Grizzly configuration is typical and my guess is that it's handier for setting to cut short tapers by feeding with the compound. Good idea to have made a gauge for setting the compound to 29.5 for threading.

My compound is usually accurately set at 29,5 deg. and left that way for any kind of turning unless the job requires otherwise. For most of my threading jobs I start by advancing with the cross slide and finish off by advancing the compound. I like being able to sneak up on final thread fit with the finer adjustments resulting from having the compound at that angle..

For really coarse threads like 8 or 10 tpi, cutting both flanks of the almost finished thread can get heavy in some materials. Personally I prefer to avoid such a wide cut so will likely do much of the coarse thread by advancing the compound.
 
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willthedancer

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#30
When I was learning machine shop, I was taught, in part, by a bunch of guys that were making chips as early as just before the turn of the century. In their day, the material of choice was hot rolled steel and it WAS STRINGY. The technique was developed to grind the threading tool such that it cut on the leading edge only and sent the chip out of and away from the generated thread.... hence the use of the compound rest and the sainted and inviolable 29.5° setting. They were highly amused that the technique was applied to everything, rather than the task that it was specifically adapted to serve... They simply never used the compound to thread anything that would generate a non-destructive chip. (And, today, neither do I.)

When carbide tools came into wide acceptance, we found that the tips of those tools would fail using the compound rest. The carbide was simply not ground to accept a side load. So, abandoning the notion of the sanctity of the compound rest, threading was accomplished using the crossfeed, only, and the problem went away.

I realize that my position is anathema on this matter, but I was taught as much WHY as HOW and it has served me well. I believe that threading using the compound is so sacred, today, simply because it got a LOT more "press coverage."


My 2¢
I respectfully disagree here.

The issue with threading is certainly chip flow across the top of the tool.

When you plunge thread with the cross slide, there are conflicting vectors on each flank of the tool, resulting in a complex collision at the center line of the tool. This leads to stacking problems and resultant tearing for one and a difficult to predict curling of the chip. Swarf is subject to cold deformation and intense work hardening, so it will damage the workpiece on contact.

Using the compound allows the chip to flow freely across the tool. The little bit of back flank interference is just to keep the form true, and the tiny bit of swarf generated is easily swept along with the majority.

That said, the use of coated carbide makes for slick surface for the chip to flow across, and much higher surface speeds, allowing for a high finish that is more scratch and tear resistant when in contact with the curled chip. It's a cheat that buys some grace when plunge threading, and often good enough.

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