threading procedure

bubsbug

bubsbug

AzB Silver Member
Silver Member
Can anyone give me any tips on how to thread using a metal lathe. I am using a 60 degree straight triangle bit. I believe my problem is in the retracking process. Once I get my starting point I set my wheel calabrator to zero. I always have my threading dial engaged, but I dont understand that thing at all. it only works or spins when I manually crank the compound slide. when the lead screw spins it seem to just ride the grove of the leadscrew instead of spinning across it, which actually makes sence. Isnt this thing suppose to tell me when to engage the leadscrew. anyways once the cut is complete, I manually back everything off and cranke compound back to my zero mark and engage leadscrew again. What am I doing wrong.
 
so far so good

You do have your compound set to 29 deg right? That way as you feed in the bit to increase the depth of cut you mostly cut the edge that the bit is moving towards. You can back off with the cross slide dial or the compound, I prefer to rezero with the cross slide and feed the new depth with the compound. As far as the thread dial is concerned it should be stationary when engaged and the threading nut is engaged. You have to re engage the half nut with the pointer at the correct indicator on the dial every time you return your carriage to the start position for the next pass. Which line or number you need to line up on is dependent on the number of TPI. See the online book I mentioned to you in an earlier post, beginning around page 160 or so. It can be very enlightening.
 
lathe threading

DaveK said:
This is a pretty good overview. The threading procedures are on page 2 :

http://www.americanmachinetools.com/how_to_use_a_lathe.htm

Dave
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I have read it many many times. in the pictures it shows the compound at 29 degrees but the cutter is still perpendicular to the work peice. I fiqures what difference does it make, perpendicular is perpendicular so I quess I didnt understand the 29 degree thing, I read it, new it, but didnt do it. So I will test it.
 
bubsbug said:
I have read it many many times. in the pictures it shows the compound at 29 degrees but the cutter is still perpendicular to the work peice. I fiqures what difference does it make, perpendicular is perpendicular so I quess I didnt understand the 29 degree thing, I read it, new it, but didnt do it. So I will test it.
Click to expand...

You set the compound at 29 deg, you make sure that the 60deg V cutter is exactly perpendicular to the surface, you then use the compound to move the cutter toward the material, not the cross slide. If you move the cross slide into the material the 60 deg cutter will cut on both sides and cause a whole lot of chatter. By using the compound, you are moving into the material at an angle so that only one side of the cutter is cutting, eliminating chatter. At the end of your cut you move the cross slide to move the cutter away from the material, move back to your starting point, using the cross slide move it towards the material stopping at the same place you had started and then use your compound again to move the cutter further into the material and then do the same procedure all over again.

Dick
 
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rhncue said:
You set the compound at 29 deg, you make sure that the 60deg V cutter is exactly perpendicular to the surface, you then use the compound to move the cutter toward the material, not the cross slide. If you move the cross slide into the material the 60 deg cutter will cut on both sides and cause a whole lot of chatter. By using the compound, you are moving into the material at an angle so that only one side of the cutter is cutting, eliminating chatter. At the end of your cut you move the cross slide to move the cutter away from the material, move back to your starting point, using the cross slide move it towards the material stopping at the same place you had started and then use your compound again to move the cutter further into the material and then do the same procedure all over again.

Dick
Click to expand...
Butabing, butabang, I think I understand it now! Momma always sayes I not very smart, but I can lift heavy objects! I was using the cross slide to move further into the material, but dont tell anyone, keep this one between us. Im leaving town tomorrow, but I certainly will practice it on Sunday. Thanks everyone for clearing the water.
 
rhncue said:
You set the compound at 29 deg, you make sure that the 60deg V cutter is exactly perpendicular to the surface, you then use the compound to move the cutter toward the material, not the cross slide. If you move the cross slide into the material the 60 deg cutter will cut on both sides and cause a whole lot of chatter. By using the compound, you are moving into the material at an angle so that only one side of the cutter is cutting, eliminating chatter. At the end of your cut you move the cross slide to move the cutter away from the material, move back to your starting point, using the cross slide move it towards the material stopping at the same place you had started and then use your compound again to move the cutter further into the material and then do the same procedure all over again.

Dick
Click to expand...
I thought I had it but I guess not. Compound is at 29 degrees and cutter is perpendicular to material. compound, cross slide, carriage slide all zeroed. Make a pass to end. Back out cross slide, manually move carrage back to zero mark, move cross slide back to zero mark, turn lathe on, move compound into material .003, hit the feed lever to make another pass and keep repeating. It sounds very simple, but Im doing something wrong because my threads look like my dog chewed them up. Lathe is at 300 rpm. Any thoughts.
 
bubsbug said:
I thought I had it but I guess not. Compound is at 29 degrees and cutter is perpendicular to material. compound, cross slide, carriage slide all zeroed. Make a pass to end. Back out cross slide, manually move carrage back to zero mark, move cross slide back to zero mark, turn lathe on, move compound into material .003, hit the feed lever to make another pass and keep repeating. It sounds very simple, but Im doing something wrong because my threads look like my dog chewed them up. Lathe is at 300 rpm. Any thoughts.
Click to expand...

When threading metal, your tooling needs to be sharp and lots of oil needs to be used. 300 rpm is way to fast, use your back gear and go as slow as the lathe will allow. I usually turn metal threads at around 35 rpm. Also take very small cuts. You can start out taking a little deeper cuts but the farther you get into the rod the shallower the cut. You need to have your cuts as close to the chuck as safely possible and you need to use a center in your tail stock. Single point threading is not easy and takes much practice. As other's have said previously, internal threading is much harder to accomplish than external also.

Dick
 
Cutting Threads

bubsbug said:
I thought I had it but I guess not. Compound is at 29 degrees and cutter is perpendicular to material. compound, cross slide, carriage slide all zeroed. Make a pass to end. Back out cross slide, manually move carrage back to zero mark, move cross slide back to zero mark, turn lathe on, move compound into material .003, hit the feed lever to make another pass and keep repeating. It sounds very simple, but Im doing something wrong because my threads look like my dog chewed them up. Lathe is at 300 rpm. Any thoughts.[/QUOTE

Follow the advise on the other posts and set the tool bit slightly below center. If cutting steel use a cutting oil with lots of sulpher in it (black cutting oil). If cutting aluminum use a fluid designed for that material. If trying to thread wood it cant be done very good with a single point tool, if at all. At least I never could. Get a router set-up and use a "live" cutter for the perfect thread.

Bob Flynn
Denali Pool Cues
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