Gunsmithing Threading Problem...

[Swampkat]

I've been having a problem threading.

Setting the compound at 29, 29.5, and 30 degrees, dial indicating the threading tool parallel to the work piece, and it has been producing threads that are off angle.

When I set the compound at 0 degrees and feed in w/ the cross slide, it produces perfect threads.

Does anyone have a clue or suggestions to what the problem could be?

 

[McLarenross]

Re: Threading Problem...

I had this problem for a while too. Are you sure your offsetting the compound 29.5* from length of the Z axis and not from 90* of it. On my Chinese lathe the protractor was marked with 0* at the center when it should really be 90* and that kept messed me up. Once I figured that our and offset it correctly my threads came out a lot better. I hope Ive explained what I mean correctly.

 

[300sniper]

Re: Threading Problem...

try 60-60.5 degrees on your compound.

 

[McLarenross]

Re: Threading Problem...

I guess thats a hell of a lot easier way to say what I meant. lol. Thanks man.

 

[Keith Johns]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">try 60-60.5 degrees on your compound. </div></div>

Bingo


It needs to be 30* from 90* to bore. Not 30* off bore.

 

[Swampkat]

Re: Threading Problem...

Got it, thanks guys.

I'm such a tard, can't believe I didn't think of that before.

 

[microsuck]

Re: Threading Problem...

And Jared, another thing you can do is thread a test piece and only using the cross slide to cut deeper. (your last few passes should only be on the cross slide anyways) It will take much longer because you are cutting on both sides of the tool, but it will eliminate the problem of having your compound off angle. Just to double check your dial on the compound.

 

[jonaddis84]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: microsuck</div><div class="ubbcode-body">(your last few passes should only be on the cross slide anyways) </div></div>

Explain this please, I do mine 100% with the compound dial, am I doing it incorrectly? The threads turn out great for the lathe Im doing them on.

 

[Bugholes]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: microsuck</div><div class="ubbcode-body">(your last few passes should only be on the cross slide anyways) </div></div>

Explain this please, I do mine 100% with the compound dial, am I doing it incorrectly? The threads turn out great for the lathe Im doing them on.</div></div> making the last pass advancing the cross slide and compound .001 will leave you a better final finish

 

[PCR]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: microsuck</div><div class="ubbcode-body">(your last few passes should only be on the cross slide anyways) </div></div>

Explain this please, I do mine 100% with the compound dial, am I doing it incorrectly? The threads turn out great for the lathe Im doing them on.</div></div>

Using the compound dial to cut threads will allow your tool to cut the lead angle of the thread putting less pressure on the tool (you're cutting mostly on the left side). Like said,cut the last few thou. with the cross slide dial and finish with a couple spring passes to clean it up.

 

[jonaddis84]

Re: Threading Problem...

Gotcha, Ill give that a try and see how it improves. Since you are advancing directly into the workpiece instead of on a 29.5 degree angle do you take less than .001 passes? I know when you get to the end you are taking the most amount of material out, so even .001 on the compound is removing a lot of material.

 

[Keith Johns]

Re: Threading Problem...

When I get to the point that Im moving the tool straight in on X for the last few passes Im turning that dial less than .001" each pass. Maybe a half thou or so, then a spring pass. While keeping it covered in cutting fluid.

I dont use cutting fluid until Im like halfway done with the threads. Just dont need it.

I speed it up on the last few passes too. About as fast as I can handle without risking hitting my shoulder. Leaves a nicer finish for me.

 

[PCR]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azshooter</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: microsuck</div><div class="ubbcode-body">(your last few passes should only be on the cross slide anyways) </div></div>

Explain this please, I do mine 100% with the compound dial, am I doing it incorrectly? The threads turn out great for the lathe Im doing them on.</div></div>

Using the compound dial to cut threads will allow your tool to cut the lead angle of the thread putting less pressure on the tool (you're cutting mostly on the left side). Like said,cut the last few thou. with the cross slide dial and finish with a couple spring passes to clean it up.</div></div>

Should have said that I do this with the compound rest set at 29.5 degrees off of 90 degrees of bore.

 

[rossneder]

Re: Threading Problem...

As I understand it going in with the cross slide is fine depending on the lathe. If solid and powerful enough all is well.

 

[PCR]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rossneder</div><div class="ubbcode-body">As I understand it going in with the cross slide is fine depending on the lathe. If solid and powerful enough all is well.</div></div>

Sure, you can feed straight in with the cross slide. It just puts more pressure and deflection on the threading tool because its cutting the threads on both sides instead of the left or leading side of the tool.

 

[Swampkat]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azshooter</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rossneder</div><div class="ubbcode-body">As I understand it going in with the cross slide is fine depending on the lathe. If solid and powerful enough all is well.</div></div>

Sure, you can feed straight in with the cross slide. It just puts more pressure and deflection on the threading tool because its cutting the threads on both sides instead of the left or leading side of the tool. </div></div>

Makes a lot of sense, thanks for the sound advice.

 

[Swampkat]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">try 60-60.5 degrees on your compound. </div></div>

Got a chance this evening to check, and 60 degrees was where it needs to be.

 

[PCR]

Re: Threading Problem...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JL1911</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">try 60-60.5 degrees on your compound. </div></div>

Got a chance this evening to check, and 60 degrees was where it needs to be.</div></div>

Yes. If you point the compound rest straight into X, then turn it to the left 29.5 degrees, you'll be there. After that, point the threading tool straight into X and feed with compound rest dial to cut threads. Like said, you'll be cutting the leading edge or flank and your threads will cut nicely and leave a good finish.