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Advice on a Compound Lead Screw

tjb

Terry
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#1
Hello to All.

Some of you may remember that I've recently posted some ?'s about a Jet P1024 look-alike that I have (Kin Shin Model KS3.5FK) and received some invaluable information from many of you. The machine now runs great and is wired properly. Thanks again.

I have what appears to be the final (hopefully) issue on this machine. The compound lead screw is very slightly bent. It's too slight to tell with the naked eye unless you know it's there, but it's bad enough to where I can only get about 90 degrees turn before it starts binding. Since I plan to use this machine primarily for threading, that's obviously not acceptable. If I remember correctly when I first started going through this machine, Ulma Doctor (Mike) suggested trying to straighten it. Mike also sent me the manual for Grizzly's G9249 lathe, which lists a similar 'looking' part for the compound lead screw: pp 75 and 76 of the manual, Reference #453, Part #P9249453, 'Cross Slide Leadscrew M15'.

Here are my challenges.
1. I'm assuming that that is the right part for the compound lead screw. Can anyone confirm if this is right or wrong?

2. I called Tech Support at Grizzly, but they can't give me actual spec's on that part to see if it matches mine. Obviously, if it won't cross over without more than moderate modifications, it won't work. Does anyone have experience with the Grizzly part and its potential crossover with a Jet P1024? It's only about $40, so it's not cost prohibitive if I have to buy it, but it's a complete waste if it doesn't fit.

3. How big a deal is it to straighten mine? Mike, you gave me some info on how to do it, but I'd prefer not to even try it until I know the status on availability for a replacement.

4. Anybody know of any other resource for buying one of these?

As always, thanks to the knowledgeable and helpful community of Hobby Machinist.

Regards,
Terry
 

RandyM

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#2
Hey Terry,

Personally, I'd not be hesitant in trying to fix your part, even if you are uncomfortable doing it. Here is the way I view it. The part is no longer usable (by your determination), so the existing part has no value and hence you can not do any further damage by making the attempt. Use a straight edge or surface plate to gage your progress. Use a hydraulic press or vise to slowly push it back into shape. You'll need to be patient and go slow and steady. Once you get to where it all is looking good, install it and test it out. You have nothing to lose, anyway you look at it, if you fail you are still in search of a replacement part. If you succeed, you'll save yourself the agony. Good luck.
 

Bill Gruby

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#3
It has been my experience that most Grizzly parts do not interchange with Jet. I tried in vain with my 9x20. Gears don't mesh correctly etc. I finally ended up making most replacements myself. Jet prices were too high in my opinion. If you need the lead screw and want to cross buy you need to buy the nut and everything else that corresponds with it.

"Billy G"
 

mikey

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#5
I would try to straighten it. If you prefer not to do that and cannot find an exact replacement then just make one from Acme threaded stock. If your nut is not excessively worn, this will result in a complete fix. If the nut is worn then you'll need to make the nut, too.
 

tjb

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#6
Hey Terry,

Personally, I'd not be hesitant in trying to fix your part, even if you are uncomfortable doing it. Here is the way I view it. The part is no longer usable (by your determination), so the existing part has no value and hence you can not do any further damage by making the attempt. Use a straight edge or surface plate to gage your progress. Use a hydraulic press or vise to slowly push it back into shape. You'll need to be patient and go slow and steady. Once you get to where it all is looking good, install it and test it out. You have nothing to lose, anyway you look at it, if you fail you are still in search of a replacement part. If you succeed, you'll save yourself the agony. Good luck.
Yeah, Randy. I'm not too uncomfortable in trying to straighten it. Just thought I'd see if it was easy and relatively inexpensive to buy one. Then I'd stick the old one in a scrap bin for a future who-knows-what project. I suspect I'll end up trying to fix this one. My shop press is pneumatic, and I've never tried to do anything quite this precise with it. I'm concerned that I won't have enough control on the foot pedal to not 'overcorrect'. I have a good heavy duty vise, so that might be a better way to go. What do you think?

Regards
 

RandyM

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#7
Yeah, Randy. I'm not too uncomfortable in trying to straighten it. Just thought I'd see if it was easy and relatively inexpensive to buy one. Then I'd stick the old one in a scrap bin for a future who-knows-what project. I suspect I'll end up trying to fix this one. My shop press is pneumatic, and I've never tried to do anything quite this precise with it. I'm concerned that I won't have enough control on the foot pedal to not 'overcorrect'. I have a good heavy duty vise, so that might be a better way to go. What do you think?

Regards

Sounds like a flawless plan. Let us know how you fair.

P.S. If you still want to use the press and are concerned about over doing it, then I'd make a fixture with adjustable stops.
 

tjb

Terry
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#8
It has been my experience that most Grizzly parts do not interchange with Jet. I tried in vain with my 9x20. Gears don't mesh correctly etc. I finally ended up making most replacements myself. Jet prices were too high in my opinion. If you need the lead screw and want to cross buy you need to buy the nut and everything else that corresponds with it.

"Billy G"
Thanks, Bill. That's exactly the kind of information I need to know. I don't have the measurements in front of me right now, but I think my leadscrew is 5 and 15/16 inches long, Acme 8 TPI, and 20 TPI for retainer ring on the hand dial end. It appears to have started with 5/8 stock but only about 1/8 inch is still that diameter (and that is about 2 inches from hand dial end). On both the leadscrew side and dial side, it is milled down. I suppose if the overall length is tolerable, I could buy (or make) the nut as well, and machine to fit for the dials as necessary. (Here's an APB for anyone who might know the overall length/major diameter of the Grizzly leadscrew.)

What do you think? (Comments from anyone else appreciated as well.)

Regards,
Terry
 

tjb

Terry
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#9
Make a new one. You got the original to copy.
Thanks, Mark. That's going to be my option of LAST resort. From what I've read and heard, I suspect I need a lot more practice before cutting Acme threads.

Regards
 

tjb

Terry
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#10
I would try to straighten it. If you prefer not to do that and cannot find an exact replacement then just make one from Acme threaded stock. If your nut is not excessively worn, this will result in a complete fix. If the nut is worn then you'll need to make the nut, too.
Mikey,

The nut's in pretty good shape, so that's the same knee-jerk option I had. (I did that on an older Harrison lathe, and it worked out great.) There's an added challenge here, however, because the overall diameter of the leadscrew is 5/8 inch, but it's milled down on both ends of about a 1/8 inch section (see my response to Bill Gruby's post above). If I end up doing it that way, I'll probably start with a slimmer piece of Acme threaded rod and build up a shoulder. Shouldn't be too difficult, but I'd still like to find one if it's out there.

Thanks for the response.

Regards,
Terry
 

mikey

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#11
Another option is to replace the bent Acme section and keep the rest - much easier and faster to do. You just need to cut the bent threaded section off, turn a pin on the end and fit it into a hole in the new threaded rod. I recommend that you silver solder it and pin it in place but this will be a permanent fix and will work like new.
 

DAT510

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#12
Terry,

With regards to you question about Grizzly G9249 fitting other similar lathes. I have a Jet 1022P. It was missing the metric treading gears. After comparing the drawings and gear tables, it looked like the grizzly gears would work. My biggest concern was potentially a different bore size. I took a chance and ordered them, and they fit perfect. I can't say the compound screw would fit, but there does appear to be some compatibility between parts. For $40 it might just be worth the time saved?
 

tjb

Terry
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#13
Another option is to replace the bent Acme section and keep the rest - much easier and faster to do. You just need to cut the bent threaded section off, turn a pin on the end and fit it into a hole in the new threaded rod. I recommend that you silver solder it and pin it in place but this will be a permanent fix and will work like new.
That's a GREAT idea! Thanks for the tip, and I'll keep that in mind.
 

tjb

Terry
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#14
Terry,

With regards to you question about Grizzly G9249 fitting other similar lathes. I have a Jet 1022P. It was missing the metric treading gears. After comparing the drawings and gear tables, it looked like the grizzly gears would work. My biggest concern was potentially a different bore size. I took a chance and ordered them, and they fit perfect. I can't say the compound screw would fit, but there does appear to be some compatibility between parts. For $40 it might just be worth the time saved?
Thanks, and that's reassuring. This biggest concern about compatibility is the 'M15' in the Grizzly's part description. I wondered out loud to the tech if that might indicate it's metric. He wasn't sure but agreed that it's highly likely. For forty bucks, we may end up finding out.

Regards
 

gregc

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#15
Before ordering grizzly I would ask about the thread pitch. I was considering buying a g0752 I had to travel to Missouri and wanted to see it before ordering. When there I noted the cross slide was approximately 0.100 per rev but not quite. I suspect it was 4 threads / cm as it was about 0.005 off. I quickly decided I'd but precision Matthews and forget grizzly. Matt at pm thought they had changed that but at least not the floor model. None of the sales people could confirm


Greg


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tjb

Terry
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#16
Before ordering grizzly I would ask about the thread pitch. I was considering buying a g0752 I had to travel to Missouri and wanted to see it before ordering. When there I noted the cross slide was approximately 0.100 per rev but not quite. I suspect it was 4 threads / cm as it was about 0.005 off. I quickly decided I'd but precision Matthews and forget grizzly. Matt at pm thought they had changed that but at least not the floor model. None of the sales people could confirm


Greg


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Thanks, Greg.

When I called tech support at Grizzly, they couldn't give me ANY specs on the part. I strongly suspect I'll end up attempting to fix my lead screw, but I'd still love to hear from someone who has a Grizzly 9249. Anybody?

Regards
Terry
 

RJSakowski

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#17
The G0752 is the VFD version of the G0602. The 602 compound lead screw is an M8-1.0mm RH Vee thread.
 

gregc

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#18
I did not scrutinize the compound slide but a 1mm pitch would be 0.039/rev. Which is close to what I saw


The cross slide had a dial for 0.100 /rev. If it was a 2.5 mm pitch this would be 0.098/rev which is what I saw. (Seems I have to do the math to remind the mind :).

I would have preferred a all metric machine that these funny approximations


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RJSakowski

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#19
The 602 cross slide lead screw has a diameter of 10mm and a pitch of 1.50mm. It is a LH Vee thread. The dial is calibrated for .060"/rev. but is actually .05906".
 

tjb

Terry
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#20
The 602 cross slide lead screw has a diameter of 10mm and a pitch of 1.50mm. It is a LH Vee thread. The dial is calibrated for .060"/rev. but is actually .05906".
Thanks, RJ.

That definitely will NOT cross over to my machine.

Regards
 

tjb

Terry
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#21
Okay, Everybody.

After reviewing everyone's input, I decided to take the following approach. Strategy 1: Try to fix the lead screw. If that failed, I've essentially lost nothing (as several have suggested). Strategy 2: If I broke it, cut off the Acme threaded rod and weld and pin on a new section. If I blew that, I'm still out essentially nothing except I would then own a remnant of Acme threaded rod that might come in handy someday. Strategy 3 (and actually an ongoing process since the beginning): Keep looking for a replacement.

I gave Strategy 1 a try in the shop today, and I'm happy to report it was quite successful. As an expression of gratitude and hopefully as a benefit to anyone else who runs into this kind of problem, I'd like to present the following pictorial documentation of the steps I took to fix the lead screw. Any of you real experts out there with suggestions on how I could have done it better, PLEASE respond for the benefit of all of us. Here we go.

Step 1: Try to identify exactly where the bend is in the lead screw. A visual examination didn't help much. The 5/8" shoulder in the middle made it challenging to lay flat, so I drew a 'plus' sign on the end of the shaft (difficult to see in the photo) and marked the points beginning at top and going clockwise 1-2-3-4. Using a surface plate, v-block and height gauge, I registered the readings in these four positions. I was careful to take all the readings on the crown of the same thread rotation. I normalized the readings so that the lowest value was exactly zero. I also took some readings further up the shaft to help me identify where the bend started. The first six attached pictures shows how I did it.

Step 2: Straighten the bend on the shop press. Since the 1-3 (vertical) dimension was far worse than the 2-4, I started there. Before moving to the shop press, I used a ruler to determine approximately how high the center of the shaft should be above the bench when still mounted on the v-block. I straightened the shaft until I achieved that point in the 1-3 dimension. Photos 7, 8 and 9 show the process.

Step 3: Assemble the compound to check preliminary results. After adjusting on the 1-3 dimension, I did a dry assembly to see how close it would be. Amazingly, the compound worked fine. If I forced myself, I could sense a very slight binding, but it's not enough to make me want to fine tune it more. (Like Yogi says, "If it ain't broke, don't break it.") I finished the assembly and called it a day (see photos 10, 11 and 12). Start to finish: about two hours.

Again, I'd like to thank all who responded with very good advice and counsel. This was a good learning experience for me and what appears to be the last step in getting this fine machine in good and complete working condition. Any suggestions on how I could have done this more efficiently? There may be a 'next time' for me or some of us other neophytes.

Regards,
Terry

P.S.: I'm not sure if I'm attaching photos correctly. If any of you have problems seeing them, let me know, and I'll give it another shot.


IMG_1245.JPG IMG_1246.JPG

IMG_1245.JPG IMG_1246.JPG IMG_1247.JPG IMG_1248.JPG IMG_1249.JPG IMG_1250.JPG IMG_1252.JPG IMG_1256.JPG IMG_1257.JPG IMG_1258.JPG
 

mikey

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#22
I took a slightly different approach and used an aluminum V-block on either end and measured the high point of the bend. Then I press, check, press and check until the bend is eliminated. I shoot for 0.001" TIR or less if I can get it. I've only done this twice so not a lot of experience with it but this worked for me.
 

tjb

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#23
I took a slightly different approach and used an aluminum V-block on either end and measured the high point of the bend. Then I press, check, press and check until the bend is eliminated. I shoot for 0.001" TIR or less if I can get it. I've only done this twice so not a lot of experience with it but this worked for me.
I thought about doing it that way, Mikey, but the 5/8" shoulder prevented that. The shoulder starts about 2" in on one side (OAL = @6"), and the bend started about 3/4" beyond it. Really wasn't enough room to place the press. Two v-blocks would certainly have been easier in most circumstances, though.

Thanks for the reply.

Regards,
Terry
 

Glenn Brooks

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#24
Yeah, Randy. I'm not too uncomfortable in trying to straighten it. Just thought I'd see if it was easy and relatively inexpensive to buy one. Then I'd stick the old one in a scrap bin for a future who-knows-what project. I suspect I'll end up trying to fix this one. My shop press is pneumatic, and I've never tried to do anything quite this precise with it. I'm concerned that I won't have enough control on the foot pedal to not 'overcorrect'. I have a good heavy duty vise, so that might be a better way to go. What do you think?

Regards
I recently had a new cross feed screw and nut made up for around $150. Best investment I ever made. Made my lathe like new.

If your screw is worn, it won't hold dimensions consistently. So sure, try to straighten, but if your not satisfied, you can have a new part made up to the exact dimensions,of the old one. And no guess work with Grizzly.

Glenn
 

f350ca

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#25
Well done Terry!
The way you did it worked as the bend was at the start of the tread.
I had a part come out of the chuck (think it was still too hot from welding and as it cooled it shark and loosened), it pushed the carriage back, bent the lead screw and broke the casting holding the nut. The bend here was in the middle of the thread so had to be straightened using v blocks and pressing between them.
Got it straight enough to use while making a new one. The acme thread was a metric dia and form with inch pitch and the adjusting thread to preload the bearings was metric. My other lathe doesn't cut metric.



Greg
 

tjb

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#26
I recently had a new cross feed screw and nut made up for around $150. Best investment I ever made. Made my lathe like new.

If your screw is worn, it won't hold dimensions consistently. So sure, try to straighten, but if your not satisfied, you can have a new part made up to the exact dimensions,of the old one. And no guess work with Grizzly.

Glenn
Thanks for info, Glenn. As you may know if you've followed the thread, I was able to straighten the lead screw and the compound is working fine now (never was an issue with the lead screw nut). It's good to know, however, that it's not impossible to have a set made.

Thanks again for the info.

Regards,
Terry
 

tjb

Terry
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#27
Well done Terry!
The way you did it worked as the bend was at the start of the tread.
I had a part come out of the chuck (think it was still too hot from welding and as it cooled it shark and loosened), it pushed the carriage back, bent the lead screw and broke the casting holding the nut. The bend here was in the middle of the thread so had to be straightened using v blocks and pressing between them.
Got it straight enough to use while making a new one. The acme thread was a metric dia and form with inch pitch and the adjusting thread to preload the bearings was metric. My other lathe doesn't cut metric.



Greg
Whoa!!! That's ugly! As you can see from my photos, mine was not bent nearly as badly as yours. From your picture, your compound looks to be just like mine. It makes sense that you have an Imperial pitch on a metric rod. That's exactly what it seemed like to me. That's the main reason I was anxious to either fix it or buy a replacement. Does anybody sell that kind of threaded rod (McMaster-Carr, etc.)? Were you able to fix the casting?

Regards,
Terry
 

f350ca

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#28
I'd be surprised if you could buy it as rod. Mine as mentioned was a metric OD forget size but 30 deg angle rather than 29 then through inch pitch on top of that.
Made a new part out of cut iron to replace the mount.


Greg
 

tjb

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#29
I'd be surprised if you could buy it as rod. Mine as mentioned was a metric OD forget size but 30 deg angle rather than 29 then through inch pitch on top of that.
Made a new part out of cut iron to replace the mount.


Greg
Beautiful work.
 

jouesdeveaux

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#30
Hi Terry
I had a similar problem on the compound rest for my Grizzley 8689. The lead screw did not rotate smoothly through 360 degs and became tight once every 360 degs. Early on, I eliminated a bent lead screw from the crowd of "suspects". To make a (fairly) long story short, the problem came down to the two discs that formed the dials attached to the end of the lead screw and to the top part of the compound rest. Their inner faces rotate against each other. The two faces that met simply were not parallel, and so there was one spot in each 360 deg rotation that significantly tightened up. The inner face of the outer dial disc was skightly raised at about "10" mils and "30" mils (on the dial). I lapped the face until it appeared to be flat. When I put the compound rest together again. It rotated smoothly through 360 degs.
Cheers,
Gerry

.[/QUOTE]
 
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