Having a problem with the quick change tool post I got from mat, I did a video because its easier for me to explain, any help would be greatly appriciated
http://youtu.be/AzaDzwhG3Bg
http://youtu.be/AzaDzwhG3Bg
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PM 1236 tool post issues
- Thread starter Blackhawk
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bvd1940
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First are you running fast enough for carbide?????
I use HSS for all but the hardest threading, you might also check if your tool bit holder is square, that might be what is out of whack?
HSS for slow cutting, Carbide fast heavy cuts.
Is that QC holder piston or wedge? Wedge is more repeatable and solid.
)
Also are you feeding with compound or cross feed?
Use your compound and set at 29.5 degrees OK?
It also helps to hand or power hone the bits.
I use HSS for all but the hardest threading, you might also check if your tool bit holder is square, that might be what is out of whack?
HSS for slow cutting, Carbide fast heavy cuts.
Is that QC holder piston or wedge? Wedge is more repeatable and solid.
)Also are you feeding with compound or cross feed?
Use your compound and set at 29.5 degrees OK?
It also helps to hand or power hone the bits.
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- Aug 12, 2013
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The tool slanting down slightly on the side to the chuck is not going to significantly impact the cut quality.
As BVD above said, the spindle speed when threading is critical. You want nice threads, use HSS and run the spindle as fast as you can control. Threads cut at 70 rpm are going to look terrible even if you get everything perfect and are using HSS.
HSS will work better at slow speeds than carbide, as carbide relies on speed and pressure to make the cut, and does not work well when cutting very small DOC. How much were you taking off on a pass when you were cutting the threads? Carbide does not like only taking off 0.005" at a pass, and will tend to skip across the surface, giving an irregular cut.
The close up of the tool you used looks like you are using a CNMG insert? You can't cut threads with that. You need a tool with a 60 degree point (CNMG diamond has an 80 degree point). A threading tool has a fairly sharp tip, the CNMG you are using has a fairly large radius on the tip (looked like a 1/32", like on a CNMG 332)
You said that you believed your setup was correct. Based upon what I have seen so far, I bet you have some other issues with your setup you haven't shown. Was your compound set at 29.5 degrees from the 90 degree point (depending on how your compound protector scale is labelled)? Did you feed with the compound while threading? How much of a cut did you feed each pass? What was your feed rate? What was your spindle speed?
By the way, I suspect the damage you showed on your carbide is because you were grinding rather than cutting. Small cuts are death to carbide, as you really need a good chip to remove the heat from the part. If you barely kiss the workpiece, you will end up eroding the tip of your carbide.
At the end you showed a 60 degree HSS you ground, which looks like it should work (although I couldn't see how much relief you ground into the tool based upon the video). Were your earlier threads with the carbide?
Here is great video on grinding a HSS threading tool (this guy was my instructor at one point):
https://www.youtube.com/watch?v=jnmFUBpmEF0&spfreload=10
He also has two previous videos on grinding a LH and RH tool bits.
As BVD above said, the spindle speed when threading is critical. You want nice threads, use HSS and run the spindle as fast as you can control. Threads cut at 70 rpm are going to look terrible even if you get everything perfect and are using HSS.
HSS will work better at slow speeds than carbide, as carbide relies on speed and pressure to make the cut, and does not work well when cutting very small DOC. How much were you taking off on a pass when you were cutting the threads? Carbide does not like only taking off 0.005" at a pass, and will tend to skip across the surface, giving an irregular cut.
The close up of the tool you used looks like you are using a CNMG insert? You can't cut threads with that. You need a tool with a 60 degree point (CNMG diamond has an 80 degree point). A threading tool has a fairly sharp tip, the CNMG you are using has a fairly large radius on the tip (looked like a 1/32", like on a CNMG 332)
You said that you believed your setup was correct. Based upon what I have seen so far, I bet you have some other issues with your setup you haven't shown. Was your compound set at 29.5 degrees from the 90 degree point (depending on how your compound protector scale is labelled)? Did you feed with the compound while threading? How much of a cut did you feed each pass? What was your feed rate? What was your spindle speed?
By the way, I suspect the damage you showed on your carbide is because you were grinding rather than cutting. Small cuts are death to carbide, as you really need a good chip to remove the heat from the part. If you barely kiss the workpiece, you will end up eroding the tip of your carbide.
At the end you showed a 60 degree HSS you ground, which looks like it should work (although I couldn't see how much relief you ground into the tool based upon the video). Were your earlier threads with the carbide?
Here is great video on grinding a HSS threading tool (this guy was my instructor at one point):
https://www.youtube.com/watch?v=jnmFUBpmEF0&spfreload=10
He also has two previous videos on grinding a LH and RH tool bits.
Last edited:
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The first indexable tool you showed is using a CCMT 32.5 style insert, I use the same tool quite often with CCGT inserts. Not sure if you actually did try using that for threading but it's only good for facing & turning since it's an 80° diamond shape insert, not good for 60° thread forms.
If you are threading soft aluminum or finer threads on steel, instead of the modified flank method (feeding with compound set at 29-29.5°), try threading with just feeding the cross slide straight in. The modified flank method is the better way to thread (arguably) since it's less wear on the cutter, less tool pressure, etc., but if you're not threading a coarse thread you can get away with feeding straight in with the cross slide on a lathe this size. Align the tool bit tip with the work using a fishtail & give it a try.
You mentioned jagged/sharp threads. If you were using the modified flank method to cut threads, that's usually a good indication of the compound angle set incorrectly. This is a common mistake with Asian lathe owners new to threading. The compound must be set 29-29.5° off the cross slide or 61-60.5° off the spindle axis.
Many (but not all) Asian import lathes do not come with a full protractor for the compound slide like older American lathes do. Most of them indicate 0° when parallel to the spindle (like the PM1236 does, I have the same lathe). So if you set 29° on the scale you are at the wrong angle for threading. You will need a protractor to set the correct angle for threading as the scale on the compound slide is useless for that.
This is what 29.5° looks like using the scale, incorrect for external threading.
This is what 29.5° looks like for threading.
As you can see the scale is useless for that on the PM1236.
I use a preset slide bevel to set the compound for threading.
If you are threading soft aluminum or finer threads on steel, instead of the modified flank method (feeding with compound set at 29-29.5°), try threading with just feeding the cross slide straight in. The modified flank method is the better way to thread (arguably) since it's less wear on the cutter, less tool pressure, etc., but if you're not threading a coarse thread you can get away with feeding straight in with the cross slide on a lathe this size. Align the tool bit tip with the work using a fishtail & give it a try.
You mentioned jagged/sharp threads. If you were using the modified flank method to cut threads, that's usually a good indication of the compound angle set incorrectly. This is a common mistake with Asian lathe owners new to threading. The compound must be set 29-29.5° off the cross slide or 61-60.5° off the spindle axis.
Many (but not all) Asian import lathes do not come with a full protractor for the compound slide like older American lathes do. Most of them indicate 0° when parallel to the spindle (like the PM1236 does, I have the same lathe). So if you set 29° on the scale you are at the wrong angle for threading. You will need a protractor to set the correct angle for threading as the scale on the compound slide is useless for that.
This is what 29.5° looks like using the scale, incorrect for external threading.
This is what 29.5° looks like for threading.
As you can see the scale is useless for that on the PM1236.
I use a preset slide bevel to set the compound for threading.
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- Mar 22, 2013
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You guys seem to have it covered.
90% of threading problem questions that I get are because the compound is set on the wrong 29.5 degrees, just like Will shows here.
Thanks for helping him out here guys! Lot of good suggestions here!
I think Will is better than I am at threading, he sent me a piece once that he machined, and the finish and detail on it was absolutely top notch!
90% of threading problem questions that I get are because the compound is set on the wrong 29.5 degrees, just like Will shows here.
Thanks for helping him out here guys! Lot of good suggestions here!
I think Will is better than I am at threading, he sent me a piece once that he machined, and the finish and detail on it was absolutely top notch!
Thanks for all the replies.
i reset the angle to 29, touched up my 60d cutter and got a much nicer thread but only with the .012 shim taking up the slop in the holder when I take it out there is to much negative rake on the front of the tool to cut a nice thread. Am I stuck with this?
fixit, I think you are right the holder is cut wrong
darkzero, I set the angle the way you mentioned and sped up to 300 rpm and just drove straight in as you suggested, worked good with the shim but not without. And yes I used hss that I ground on a grinder.
and to whoever said I probably chipped my insert taking a light cut you are correct lol, that's exactly what happened,
happy thanksgiving, hope you all have a great weekend, I'll be back in the garage working on my gun barrel
lanham
i reset the angle to 29, touched up my 60d cutter and got a much nicer thread but only with the .012 shim taking up the slop in the holder when I take it out there is to much negative rake on the front of the tool to cut a nice thread. Am I stuck with this?
fixit, I think you are right the holder is cut wrong
darkzero, I set the angle the way you mentioned and sped up to 300 rpm and just drove straight in as you suggested, worked good with the shim but not without. And yes I used hss that I ground on a grinder.
and to whoever said I probably chipped my insert taking a light cut you are correct lol, that's exactly what happened,
happy thanksgiving, hope you all have a great weekend, I'll be back in the garage working on my gun barrel
lanham
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- Aug 12, 2013
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- 858
well the good news is that the cheap Chinese tool holders only cost $17.50.
http://www.shars.com/products/view/1509/Turning_and_Facing_Holder_1_Type_201
The bad news is they are only worth $16....
But as you have discovered, the cheap QCTP isn't all that great. Put a new Dorian or Aloris QCTP set on your shopping list, and buy them next time they are on sale. You will be happy you did.
Full disclosure: while I have used Aloris on machines in the past, I am suffering with a cheap knockoff now. It is on the shopping list, but other more critical things keep rising to the top....
I like this set because you don't end up paying for a bunch of strange tool holders you will never use, unlike some of the way more expensive sets:
http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=30822329&PMAKA=404-2304
wait for an Enco 20% off coupon, and it is almost affordable....
EDIT: I just remembered I had bought a shars BXA #1 tool holder to see if it was acceptable, but I hadn't used it yet. So i just went out to the garage and put a DTI and mic on it to see if it was good.
Mic results: slot is consistant within 0.0009" of top and bottom surface along the length of the slot. Width of holder is within 0.0004" of the ground back face of the dovetail slot. Seems decent, especially given it is 1/3-1/4 the price of an Aloris holder.
The DTI results really just showed me that my cheap Grizzly piston type QCTP is really...well...cheap.
With the shars holder mounted, I ran it along the Z axis, and the slot is dead flat, no slope at all. So far so god.
Than I ran it in and out on the Y axis. 0.010" in 3" of travel. Hmmm. That means that my tool height changes as you turn a piece. Not critical, but disturbing. That 0.010" variation is due to the dovetail being cut slightly crooked on the Grizzly tool post. All my tool holders gave me that same measurement.
Guess that Aloris moving up the list....
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The tool holder could have a slot cut in it that is not square. But first check to see if the sharp corner of the tool bit is hanging up on a not sharp corner in the tool holder. And anyway, it does not amount to any problem at all, just make sure the tool bit is set-screwed down tight, that is all that matters…Good Luck, Dave.