Gunsmithing Jet Lathe problems (threading)

jonaddis84

jonaddis84

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Jan 27, 2009
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#1
Let me start off by saying I am no expert when it comes to lathes, but Im slightly better than a novice... I guess would describe me.

Second. The lathe Im using is in our "gunsmith" shop at the smallest Gander Mountain in the country (literally). It never ever got used by any of the actual gunsmiths we employed, it was always more of a showpiece than anything, to make them look like they knew what they were doing. It, AFAIK, has never been trued or properly setup. It does cut straight if I have the 3-jaw and the other end in a center, probably within .0005 over a 10" span.

Now to my problem. Ive threaded a few barrels now with it, the threads have never turned out beautiful, but they work. They are concentric to the bore and stuff threads on and off, so I WAS happy. Well I decided to redo my first attempted job which is a Savage MKII 22lr, I wanted the bbl shorter anyway.

Side note, I found out why my threads never looked great was my tool height was not set on center well enough and it ended up ruining the threading tool.

So onto my problem tonight. I got all my major and minor diameters cut and everything just fine. Set up the lead screw to 28tpi, set the rpm to 70, switched it from turning to threading and zeroed my threading tool on the dial indicator.

Went in .002" and made the first pass, looked like 28tpi so I was good. Went in another .002" and another pass, still looked good. Went in another .002" and this time it put the threads in between the previous ones and boogered it all to hell! I aways make sure Im pressing firmly down on the lead screw clamp lever (lack of proper terminology), so it wasnt that that slipped or anything.

So before I screwed up another 1/2" of my barrel taking it dangerously close to the legal minimum I decided to stick a chunk of 1/2" bar stock in there and see if it would repeat the problem. Same thing over and over again.

The best explanation I came up with is that the lead screw clamp has too much play in it and it ends up placing the carriage a few thou off each time I clamp it down. Anyone ever experience this and have a fix for me?

And just a shot in the dark, if anyone is in the Toledo,OH area and has a shop and willing to show me a few things that would be awesome!
 
#2
Re: Jet Lathe problems (threading)

You're saying the lathe is like new or new??? If not then perhaps your half nuts aren't grabbing onto the leade screw in the same place each time. I have left my carriage locked in, stopped it, backed out my crosslide feed and reversed lathe to return and take another pass. This would let you know if once you are sure you are locked tight to leade screw that it is or isn't halfnut engagement.

Other possibility is what kind of toolpost, toolholder setup are you using???? Rocker type, 4 way type common to the Jets and others or a quick change such as Aloris???? Are you solid and sure your bit isn't moving?????

Edit to add another question that you didn't mention...Are you advancing your depth with cross slide or compound? Is your compound set at 29*? You should be advancing depth with compound and not crosslide! Just in case you haven't been????

Also are you grinding HSS???? Inserts?????

One can only guess via the net with absolutely no idea of setup, experience etc etc etc.

HTH

Respectfully,
Dennis
 
#3
Re: Jet Lathe problems (threading)

How experienced are you on a lathe? Did you watch the spinning numbers on the carriage while you were locking in the thread lever.
 
#4
Re: Jet Lathe problems (threading)

Its not new, I believe it may have come to us used.

It has a basic tool post, not aloris type, fixed height, I have to shim my tools to correct height. I did check and double check that the tool post was tight as hell, and that the compound rest nuts were very tight. Im 99% sure that its not a matter of the tool moving around.

Maybe not experienced enough, what do you mean by the spinning numbers? There is the dial numbered 1-4 on the carriage that rotates as the carriage moves?
 
#5
Re: Jet Lathe problems (threading)

Yes those are the ones I was speaking of. Make sure that you start the threads on the same number each time. It should spin till you engage your threading lever.
 
#6
Re: Jet Lathe problems (threading)

It will revolve or 'move' when the carriage isn't locked in but will stop rotating once you have locked your halfnuts onto the leade screw!
 
#7
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">I had this problem several years ago and found it to be my thread dial gear. For threads that were a multiple of 8 it was OK, for all others, the same problem you describe.

With the half nut engaged is there slop / movement in the carriage when you try to move the hand wheel for and aft? A very small amount is OK.

On a test bar try cutting threads that are a multiple of 8, like 16tpi and see what happens. If the threads cut fine, I'd suspect the thread dial or thread dial gear. You are picking up the same # on the thread dial each time aren’t you? I use #2 on the thread dial 99% of the time.
</div></div>

There is a slight amount of slop when the half nut is engaged, Id estimate .002-.004", there is so much backlash in the carriage travel wheel its hard to tell.

Im not sure what you mean by the same number on the thread dial. This lathe to set the TPI There are two levers for the feedrate, a lettered lever and a numbered lever. To get 28tpi I set it on "E" and "8".
 
#8
Re: Jet Lathe problems (threading)

Ahhhhhhhh, obviously I wasnt experienced enough. I dont know how I got so lucky on the first few attempts that I never had this happen!

So when the lead screw is turning, the carriage is still, that dial will rotate, then I need to engage the halfnut on the same number each time just to confirm?

This is why I wish I couldve learned this operation from watching someone instead of trying to teach myself. Now I feel like a total jagoff.
 
#9
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body">Ahhhhhhhh, obviously I wasnt experienced enough. I dont know how I got so lucky on the first few attempts that I never had this happen!

So when the lead screw is turning, the carriage is still, that dial will rotate, then I need to engage the halfnut on the same number each time just to confirm?

This is why I wish I couldve learned this operation from watching someone instead of trying to teach myself. Now I feel like a total jagoff. </div></div>

Bingo!!!! I use 1 cause I can't count as far as Roscoe!
 
#10
Re: Jet Lathe problems (threading)

Ive got it now, this is a load off, I thought for sure there was something wrong with the machine, but I guess just the operator is broken!

Can you explain what the thread dial does....like why you would engage it at different numbers?

And thank you all so much for the quick help, and not hurting my feelers for being stupid
crazy.gif
 
#11
Re: Jet Lathe problems (threading)

Alrighty, well Ill see if I can count to 2 and use that every time now! I wish I could go in right now and redeem myself. I was beginning to think I was going to have to pay ADCO to fix my mistake! I probably couldve saved myself time, money, and headaches by just paying them the lowly $65/bbl, but it just feels better to do it myself, especially if I can get them looking as nice as the pictures I see of you guys' work.
 
#12
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">

Bingo!!!! I use 1 cause I can't count as far as Roscoe! </div></div>

same here. i always engage the half nut at "1" even when any number will work for the thread pitch. right now, i am trying to figure out how to afford eliminating using half nuts altogether in the near future
wink.gif
.
 
#13
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body"> right now, i am trying to figure out how to afford eliminating using half nuts altogether in the near future
wink.gif
. </div></div>

Ok grasshoppa,.....now listen closely and pleeeezzzze trust me on this, it is for your own good!!!!!!!!!!! Clean the leade screw completely of grease in a short section......Then clean the halfnuts really really good. Now......I know you just might question my intentions on this.....but....well.....it is for your benefit...slop a bunch of your favorite bedding compound on the part of the leade screw you should have degreased properly if you were listening....then move carriage to this spot so halfnuts are centered on the bedding compound......now I know you are starting to wonder my intent but slam them sumbitchin halfnuts down just as tight as you can on the leade screw!!!!! I mean bitch slap them suckers until the bedding ooooooozzzzzzeeesss out all around. Nooooooowwwwwww, call me in the morning and tell me you don't need to watch where/when you engage.....again 'trusssstttttt meeeee'.
wink.gif





ahhhhhhh......I always feel better after helping someone with good advice!!! Life is good.lol Oh, YEA, I am bored!!
 
#15
Re: Jet Lathe problems (threading)

Wow, wish I wouldve seen that video before I did anything. Very informative. Another thing I wasnt doing right was the compound rest. I have it at zero degrees and just used the crosslide to move in.
 
#16
Re: Jet Lathe problems (threading)

A rule of thumb is to use even numbers for even numbered threads and odd for odd numbered threads.

That's how I learned and I haven't had any problems so far.
 
#17
Re: Jet Lathe problems (threading)

I recently was threading 24 tpi and during a practice run I engage the half nuts on all the even threads just to check and see how it came out so I knew how the lathe was working. It came out good on all even numbers and I found out that my natural rhythm when threading came out great to engage on 2 and 4 with little down time between cuts or time to day dream
sleep.gif
 
#18
Re: Jet Lathe problems (threading)

Interesting, we have a Grizzly at school that is completely unreliable in this very same manner.

The ONLY way to thread on it is to make a pass,
But, DON'T disengage the threading handle, just back out the cross feed and stop the lathe.

Run it backwards (essentially threading in reverse) to your starting point.

Run the cross feed back in to zero, advance the compound and make another pass.


Essentially you are having to "pick up threads" with each pass.
What a PITA!

 
#19
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"> Another thing I wasnt doing right was the compound rest. I have it at zero degrees and just used the crosslide to move in. </div></div>

That's what was killing your tool.
 
#20
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RADcustom</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"> Another thing I wasnt doing right was the compound rest. I have it at zero degrees and just used the crosslide to move in. </div></div>

That's what was killing your tool. </div></div>

So say Im cutting 1/2-28. I cut my major diameter to .496 as per thread chart, I cut my relief to the minor diameter of .456. This means I need to cut the threads .020 deep. Does that also correspond to how far I need to dial the compound in?

This lathe has quite a bit of backlash in every dial, several thousandths. Will I be good enough using the handle markings or should I have a dial indicator setup on it?
 
#21
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RADcustom</div><div class="ubbcode-body">A rule of thumb is to use even numbers for even numbered threads and odd for odd numbered threads.

That's how I learned and I haven't had any problems so far. </div></div>

That's the rule that we'd been taught...but...

To be completely safe across all properly working lathes.

Pick one number, doesn't seem to matter, 1-4 and forever use that one number.

Doesn't seem to matter what pitch threads I've ever cut, I've always used #4 on every lathe, every time, and never had a problem.

Just cause I'm paranoid doesn't mean the "thread crashing Gods" aren't out to get me.
eek.gif
 
#22
Re: Jet Lathe problems (threading)

<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: RADcustom</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"> Another thing I wasnt doing right was the compound rest. I have it at zero degrees and just used the crosslide to move in. </div></div>

That's what was killing your tool. </div></div>

So say Im cutting 1/2-28. I cut my major diameter to .496 as per thread chart, I cut my relief to the minor diameter of .456. This means I need to cut the threads .020 deep. Does that also correspond to how far I need to dial the compound in?

This lathe has quite a bit of backlash in every dial, several thousandths. Will I be good enough using the handle markings or should I have a dial indicator setup on it? </div></div>


Not necessarily, it depends on how the dial is numbered. I always cut the major and thread to fit.

A dial indicator wouldn't hurt.

By dialing in straight you are forcing the tool to cut on both angles not leaving anywhere for the chip to go. It loads the tip of the tool and breaks the point.
 
#23
Re: Jet Lathe problems (threading)

That makes sense. That probably also explains why on my previous jobs, after I finished threading, the major diameter grew to over .500 and I had to file down the OD in order for the part to thread on.

When you say thread to fit, you just go in .001 at a time until whatever youre threading for will thread onto the part? Dont even worry about actual depth of cut? The trigonometry definitely says that the depth of cut perpendicular to the piece will not correspond to the movement of the compound dial.

Still feel like an idiot for not researching this process more before I jumped on the machine.
 
#24
Re: Jet Lathe problems (threading)

<span style="font-weight: bold">my guesses in bold</span>

<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: RADcustom</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"> Another thing I wasnt doing right was the compound rest. I have it at zero degrees and just used the crosslide to move in. </div></div>

That's what was killing your tool. </div></div>

So say Im cutting 1/2-28. I cut my major diameter to .496 as per thread chart, I cut my relief to the minor diameter of .456. This means I need to cut the threads .020 deep. Does that also correspond to how far I need to dial the compound in?
<span style="font-weight: bold">
No, the compound is at 30 degrees (half the 60 degees of a V-hread) SIN 30 = 0.5, so the compound moves half the distance in as the dial indicates.</span>

This lathe has quite a bit of backlash in every dial, several thousandths. Will I be good enough using the handle markings or should I have a dial indicator setup on it?

<span style="font-weight: bold">If you back out the cross slide enough so that you come back to your zero going in, then the backlash doesn't matter and you will repeat properly.

The compound, only goes in so the back lash isn't a problem there.

I try to back the cross slide out quickly about two turns and simultaneously kill the feed. That way it clears most every shoulder that I'm trying to thread to and doesn't leave a continuous groove at the last thread as just killing the feed would do.
</span>
</div></div>
 
#25
Re: Jet Lathe problems (threading)

With your compound set @ 29* the angle moving into the work is not full value of your dial numbers. If you move it .005 depending on thread it might only move .004 into the work piece. Would have to go dig out a threading chart but you might need .024 or .025 total depth on compound to obtain a .020 thread depth. Wear, slop, slack will change that some. Until you know the lathe really well you are working with you need to pay attention.

Also if you leave your halfnuts/carriage locked in and reverse lathe there is no need to keep backing out the compound, just back out your crosslide. This eliminates getting slack out and correctly resetting both feeds each time. Just proceed with a deeper depth after setting your crosslide dial back to zero if you zeroed it or whatever number,reference point you started with. Might sound complicating in trying to explain with several paragraphs but is easier in doing then saying, at least for this digitally challenged old man.
smile.gif


Plunging in the carriage feed probably swaged/pushed metal to the top of thread and caused the increase in diameter?
 
#26
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body">That makes sense. That probably also explains why on my previous jobs, after I finished threading, the major diameter grew to over .500 and I had to file down the OD in order for the part to thread on.

When you say thread to fit, you just go in .001 at a time until whatever youre threading for will thread onto the part? Dont even worry about actual depth of cut? The trigonometry definitely says that the depth of cut perpendicular to the piece will not correspond to the movement of the compound dial.

Still feel like an idiot for not researching this process more before I jumped on the machine. </div></div>

Some people go their whole life and never bother to learn the "right" way. You're way ahead.
 
#27
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">
Also if you leave your halfnuts/carriage locked in and reverse lathe there is no need to keep backing out the compound, just back out your crosslide. This eliminates getting slack out and correctly resetting both feeds each time. Just proceed with a deeper depth after setting your crosslide dial back to zero if you zeroed it or whatever number,reference point you started with. Might sound complicating in trying to explain with several paragraphs but is easier in doing then saying, at least for this digitally challenged old man.
smile.gif

</div></div>

Ive got you. That video posted above showed what you mean well. Once you start moving the compound dial in you dont ever back it out. Just disengage the half nut in the relief, back out the crosslide to clear the peaks, and move the carriage down. Then reset the crosslide to zero, and move the compound in the desired cut depth, and re-engage the half nut.

Cant wait to make some pretty threads in the morning now.

Cant say thanks enough to everybody for walking me through this! If I ever find my way into any of your shops someday Ill bring the beer!
 
#28
Re: Jet Lathe problems (threading)

Success! It took a little playing around with some aluminum first, but I figured it out. The dial has numbered divisions 1,3,5,7 and 8 total divisions on it. I just figured Id use 1, but that didnt seem to work out for me. So I played around and it turned out any of the even divisions worked for 28tpi.

Here is a pic of some bad threads I did before and somehow got lucky I didnt wipe them out completely when I wasnt paying attention to the thread dial, they still worked believe it or not! The rest are the Savage Mark II I finished up today. Turns out I guess I didnt use stainless for the thread protector like I thought I did, the oven brought the rust out real quick...guess Ill have to spray the inside of the thread protector after all. I shouldve cleaned the gunk out of the threads so you could see them better.

bad_1.jpg

threading_1.jpg

threading_2.jpg

threading_3.jpg

threading_4.jpg

threading_5.jpg

threading_6.jpg

threading_7.jpg

threading_8.jpg
 
#29
Re: Jet Lathe problems (threading)

I recently started getting the hang of it also, take a look at Bob's channel on YouTube and find his threading series, it cleared it up for me and I knocked out some good threads after watching. Nothing beats turning out your own work and have it look right!! Bob Pastor
 
#30
Re: Jet Lathe problems (threading)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mark Housel</div><div class="ubbcode-body"><span style="font-weight: bold">my guesses in bold</span>

<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: RADcustom</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body"> Another thing I wasnt doing right was the compound rest. I have it at zero degrees and just used the crosslide to move in. </div></div>
At 30 degrees the compound only move half the distance indicated on the dial, but reduces the diameter by the amount indicated. So .020 on the dial means .020 off the diameter



That's what was killing your tool. </div></div>

So say Im cutting 1/2-28. I cut my major diameter to .496 as per thread chart, I cut my relief to the minor diameter of .456. This means I need to cut the threads .020 deep. Does that also correspond to how far I need to dial the compound in?
<span style="font-weight: bold">
No, the compound is at 30 degrees (half the 60 degees of a V-hread) SIN 30 = 0.5, so the compound moves half the distance in as the dial indicates.</span>

This lathe has quite a bit of backlash in every dial, several thousandths. Will I be good enough using the handle markings or should I have a dial indicator setup on it?

<span style="font-weight: bold">If you back out the cross slide enough so that you come back to your zero going in, then the backlash doesn't matter and you will repeat properly.

The compound, only goes in so the back lash isn't a problem there.

I try to back the cross slide out quickly about two turns and simultaneously kill the feed. That way it clears most every shoulder that I'm trying to thread to and doesn't leave a continuous groove at the last thread as just killing the feed would do.
</span>
</div></div> </div></div>
 
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