# Broken threads on the QCTP of my compound slide



## better-lathe-than-never (May 1, 2022)

I have a 9x20in Jet BD-920N mini lathe.   I installed an AXA Tool holder with the M8 tool post that I drilled and tapped myself.   Apparently I did a sloppy job in that and now I can't tighten the tool post in place making it impossible to run the lathe.   I'll post photos of my compound slide, but it's a standard on onthe 9x20 Jet lathe.

Is there a way to make this more ridgid or do I have to purchase a new compound slide body?


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## homebrewed (May 1, 2022)

I ran into something like that with my mini lathe.  It turns out that the screw hole used to attach the tool holder is drilled/tapped all the way through.  If you use a screw that's too long it will go all the way through the compound and fetch up against the cross slide, locking the compound in place.  Maybe that's what you are encountering?


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## better-lathe-than-never (May 1, 2022)

homebrewed said:


> I ran into something like that with my mini lathe.  It turns out that the screw hole used to attach the tool holder is drilled/tapped all the way through.  If you use a screw that's too long it will go all the way through the compound and fetch up against the cross slide, locking the compound in place.  Maybe that's what you are encountering?


You know... it's possible - it doesn't seem to find bottom and snug up as it should.   I'll see if I can bottom it out and try to get it snug against the cross slide.


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## Cadillac (May 1, 2022)

If the thread is stripped it looks like the thread on your post is necked down. Make a new post with a larger thread. Retap compound and make sure your not to long.
 I have the same lathe and the compound has been replaced with a solid tool post riser. Makes machine ALOT more rigid.


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## homebrewed (May 2, 2022)

better-lathe-than-never said:


> You know... it's possible - it doesn't seem to find bottom and snug up as it should.   I'll see if I can bottom it out and try to get it snug against the cross slide.


Be careful, you don't want to damage the top of your cross slide.  A quick way to determine if that's what is going on:  install the screw without the QCTP and measure how much sticks out when it (lightly) hits bottom.


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## better-lathe-than-never (May 2, 2022)

After closely examining the part, I am now certain that the thread in the top slide tool rest is stripped/broken.  Others here were recommending I make a new stud, etc - I don't have a functioning lathe so how can I do that...   I'm thinking about just drilling/tapping a hole from the back through the top of the slide and through the tool post itself to immobilize it.


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## Cadillac (May 2, 2022)

Will a off the shelf bolt get you locked. Then make new stud then retap. My thought and I could be wrong is you would be taking away strength in the wrong area. And not fully solving the problem, the shaft will not be secure enough. Tool post will move!
 Rethreading is gonna fix it the right way to get you a solid of a connection as it’ll allow.


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## better-lathe-than-never (May 2, 2022)

Cadillac said:


> Will a off the shelf bolt get you locked. Then make new stud then retap. My thought and I could be wrong is you would be taking away strength in the wrong area. And not fully solving the problem, the shaft will not be secure enough. Tool post will move!
> Rethreading is gonna fix it the right way to get you a solid of a connection as it’ll allow.


I don't follow what you're saying:  I cannot use my current lathe - the tool will not hold fast, so I cant make anything with it. 

UPDATE: Oh I guess you're saying:  find a 9/16'' bolt to temporarily immobilize the tool-post and make a bigger stud...  that won't work because it's the thread in the cast iron body that's bad, not the stud.

Would welding that cast iron to that steel stud be an option (at least temporary)?   Just to immobilize that tool post under that top slide?   I don't know how cast iron would react when welding -

I really screwed myself, because I am unable to find a replacement compound slide body - I thought LMS had the replacement part, but they told me it won't fit...  sent email to Grizzly - waiting.  If I can't find a replacement (Plan B) then I have to be very careful with that brick that I've got.


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## stupoty (May 2, 2022)

better-lathe-than-never said:


> After closely examining the part, I am now certain that the thread in the top slide tool rest is stripped/broken.  Others here were recommending I make a new stud, etc - I don't have a functioning lathe so how can I do that...   I'm thinking about just drilling/tapping a hole from the back through the top of the slide and through the tool post itself to immobilize it.



Re tap the hole to bigger thread, use a bolt or threaded rod and make a temporary tool clamp from flat piece of steel and some packing blocks (can't remember the name of this style of tool mount , was very common on old UK lathes) or refit the four way tool holder.

Stu

edit - example of a clamp style tool holder on a small lathe,






						Grayson Lathes
					

Small English lathes by a London Compnay, Gray & Son. Re-badged Randa lathes



					www.lathes.co.uk


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## ttabbal (May 2, 2022)

If you have a mill, it would help make sure you drill/tap straight. Or a drill press? I would remove the top of the compound to do the job so you don't get chips in the sliding surfaces. My compound (PM1127) came with an M10 hold down. I wouldn't want to go smaller than that. I made a new stud as well, that has a wider section in the middle. So it can tighten against the compound top to ensure everything is good before installing the QCTP. For now, just use a bolt or bit of all-thread to hold the QCTP so you can make a new stud or whatever as needed.


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## Cadillac (May 2, 2022)

Check ereplacement parts. They show 3 in stock at 180.00.


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## homebrewed (May 2, 2022)

Even my little 7x12 uses an M10 bolt for the toolpost mount.  If you've got a drill press you should be good to go (assuming you've got the right drill and an M10 tap).  You can chuck a smaller but close-fitting drill in the drill press to align the top slide -- drop the chucked-up drill in the hole.  Once aligned clamp it down, switch to the drill you need for your M10 threaded hole and go for it.

Feed slow when enlarging a hole drilled in cast iron.  It tends to pull drills into pre-drilled holes.  Also, you need to keep in mind that you can get both M10-1 and M10-1.5 bolts.  They will require slightly different-sized holes for tapping.


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## homebrewed (May 2, 2022)

homebrewed said:


> Even my little 7x12 uses an M10 bolt for the toolpost mount.  If you've got a drill press you should be good to go (assuming you've got the right drill and an M10 tap).  You can chuck a smaller but close-fitting drill in the drill press to align the top slide -- drop the chucked-up drill in the hole.  Once aligned clamp it down, switch to the drill you need for your M10 threaded hole and go for it.
> 
> Feed slow when enlarging a hole drilled in cast iron.  It tends to pull drills into pre-drilled holes.  Also, you need to keep in mind that you can get both M10-1 and M10-1.5 bolts.  They will require slightly different-sized holes for tapping.


Before you start enlarging holes:  one potential issue is the mounting hole in your QCTP.  You might need to either drill that out (if that's possible) or make/buy something that's compatible with the size of bolt or stud you use......


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## ericc (May 2, 2022)

ttabbal said:


> If you have a mill, it would help make sure you drill/tap straight. Or a drill press? I would remove the top of the compound to do the job so you don't get chips in the sliding surfaces. My compound (PM1127) came with an M10 hold down. I wouldn't want to go smaller than that. I made a new stud as well, that has a wider section in the middle. So it can tighten against the compound top to ensure everything is good before installing the QCTP. For now, just use a bolt or bit of all-thread to hold the QCTP so you can make a new stud or whatever as needed.


This is the way I would do it.  In fact, I did a similar job by buying a used (but good) tap.  Be really careful.  You will only get one chance.  Not really...if you mess up, you can do the compound replacement with a solid block trick.  That will work in case you goof up.  I would not attack it with a welder, even though I know how to weld cast iron.  Wrong application of a tool.


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## better-lathe-than-never (May 3, 2022)

Ok - was able to reasonably stabilize my current tool post last night.   I mounted the current stud in the lathe chuck and proceeded to cut fresh threads on one end of it on the unthreaded part - then I just cut off about 1/4'' off the end.  It found new 'meat' and I was able to at least temporarily secure my QCTP in place to make the new stud.

So, currently, I have a 9/16'' 18tpi hole that I want to rethread to 5/8'' 18tpi.  I have a 5/8'' steel rod that I'd like to use to make the new stud.  Was looking at the machinists charts trying to determine the proper OD of the rod for external threading.   Found this:




__





						ANSI External Screw Threads Size Tolerances Chart
					

ANSI/ ASME EXTERNAL Screw Thread Size Chart. All units are in inches. Unified Screw Threads per. ANSI/ASME B1.1-1989 (R2001), R2001) Nomenclature, are used. Acceptability criteria are described in ANSI/ASME B1.3M-1992 (R2001).



					www.engineersedge.com
				










What should I turn the OD of that 5/8'' rod down to to properly thread it to 5/8'' 18 tpi?


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## better-lathe-than-never (May 3, 2022)

homebrewed said:


> Before you start enlarging holes:  one potential issue is the mounting hole in your QCTP.  You might need to either drill that out (if that's possible) or make/buy something that's compatible with the size of bolt or stud you use......


Understand - I plan on enlarging the hole to 5/8'' ID and threading the bottom of the new stud to fit that, and then turning down the body of the stud to fit the 9/16'' +/- hole in my QCTP...  Just hope this rookie is up to this task.


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## ttabbal (May 3, 2022)

You want OD to be in the range of major diameter. Ideally, you then measure pitch diameter with a thread mic, thread wires, or other devices. You can also try to thread the mating part on it to match. Just grabbing a nut could throw it off if the tolerance stacks incorrectly. So it might fit the nut, but not the mating part. Just something to be aware of.


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## better-lathe-than-never (May 3, 2022)

I just have the basic HSS threading set - I don't have any thread mic.  What I'm really looking to know with this 5/8'' rod is:  do I run the 5/8 die on it as is or should I turn it down to say .6230 or .6240... etc


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## ttabbal (May 3, 2022)

Thread wires are cheap. You can use a mic or even a caliper to measure them. But this is a one time thing really. So if you don't want to get them, get as close as you can. 

When you say HSS threading set... Tap/die set? They should cut close enough. I thought you were going to single point the threads as you were using a lathe, but a die would work. It might be tough to run on, most of the sets you get locally are really intended for repair not cutting new threads. They can do it though. Or get close with single point and run the repair die over it.


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## better-lathe-than-never (May 3, 2022)

ttabbal said:


> Thread wires are cheap. You can use a mic or even a caliper to measure them. But this is a one time thing really. So if you don't want to get them, get as close as you can.
> 
> When you say HSS threading set... Tap/die set? They should cut close enough. I thought you were going to single point the threads as you were using a lathe, but a die would work. It might be tough to run on, most of the sets you get locally are really intended for repair not cutting new threads. They can do it though. Or get close with single point and run the repair die over it.


I am not capable of running single point threading....   My threading dies are all I have at this point.


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## woodchucker (May 3, 2022)

so I have some stainless foil.. it would work.
I assume you don't have it. But what I would do to get you by so you can redo a new bolt:
I would wrap the stud in tin foil. wrap it carefully using a tooth pick to tighten up the thread.

Then make a new stud.
if it doesn't work, consider loctite perm or bearing to hold the stud in, redo  your stud, then heat the old stud and remove.


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## stupoty (May 3, 2022)

better-lathe-than-never said:


> I am not capable of running single point threading....   My threading dies are all I have at this point.


do you have some scrap material to do some tests with ?

Stu


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## woodchucker (May 3, 2022)

stupoty said:


> do you have some scrap material to do some tests with ?
> 
> Stu


and you can even start with plastic, delrin.. then aluminum until you get some confidence. Then repeat with steel, but take very  small cuts, since the other material will spoil you.


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## better-lathe-than-never (May 3, 2022)

stupoty said:


> do you have some scrap material to do some tests with ?
> 
> Stu


Yes - I have about 12'' steel rod I can test the die on as well as a steel plate that I can use to test the tap on.  Realistically, I'm not going to learn single threading and then do that accurately on a new stud - it's too much too soon.


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## Larry$ (May 3, 2022)

If you are using rethread dies (Hex) it will go a lot easier to reduce the work a bit. From your chart .616  minimum diameter would be a good starting size. Put a generous chamfer on the end of the stock to ease starting. You really should be using a round die with adjustment screws. You can buy a quality one from McMaster-Carr and get it in a day or two. But you will also need a round die holder to use it. 
At any rate, unplug the lathe, put the work in your lathe chuck and your drill chuck in the tailstock. Open the drill chuck fully so only the outer edges touch the die holder. The idea is to ensure that the threading gets started perpendicular to the work. Lock the tail stock in place. Advance the quill until the drill chuck is snug against the end of the work. Use lots of treading or cutting oil. Rotate the lathe chuck using a wrench on the jaws for leverage at the same time maintaining pressure on the die with the quill advancing on the tail stock. Back the die off when it gets tight to break the chips. 

It is possible to get it done with a hex die but the round adjustable dies will give better results. You can thread at the most open size on the die and try the fit in the matching hole. If too tight just adjust the set screws on the die and run it again.


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## better-lathe-than-never (May 3, 2022)

Larry$ said:


> ... round adjustable dies will give better results. You can thread at the most open size on the die and try the fit in the matching hole. If too tight just adjust the set screws on the die and run it again.


Yes, I have a decent round adjustable threading die with the holder.   I'm familiar with the technique you describe above - and will give it a go.


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## Larry$ (May 3, 2022)

better-lathe-than-never said:


> I'm familiar with the technique you describe above


See, you didn't need any help, just go for it.


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## woodchucker (May 3, 2022)

better-lathe-than-never said:


> Yes - I have about 12'' steel rod I can test the die on as well as a steel plate that I can use to test the tap on.  Realistically, I'm not going to learn single threading and then do that accurately on a new stud - it's too much too soon.


you'd be surprised how easy and quickly you can learn to single point thread. Especially big threads that you can create a landing point with (a place to stop easily, an undercut).  My first threads were surprisingly good.


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## better-lathe-than-never (May 3, 2022)

woodchucker said:


> you'd be surprised how easy and quickly you can learn to single point thread. Especially big threads that you can create a landing point with (a place to stop easily, an undercut).  My first threads were surprisingly good.


I would love to learn it - it's on my radar to start learning it soon.


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## Larry42 (May 3, 2022)

better-lathe-than-never said:


> it's on my radar to start learning it soon.


No time like the present! Tonight would be a good time. It really isn't very difficult. Metric on an imperial leadscrew is somewhat of a PIA but taken slowly not all that bad either. Go to the YouTube University, Joe Pie's site. Watch his videos on threading.


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## Bi11Hudson (May 3, 2022)

The basic premise here is (was) a fairly common problem on the earlier versions of most of the smaller lathes. It is in no wise limited to the Jet  It sounds like you crossed up metric and imperial threads trying to mount a newer type tool post. If I understand the damage correctly, the simplest solution is to replace the center post with the next larger size and drill/thread the top or compound slide to match. If the compound is disabled, perhaps the top slide is still usable by adding spacers.

I have a Grizzly G1550, an almost exact duplicate of the Jet. When I mounted the AXA tool holder, I had to make a special post for the tool holder to fit properly. That has improved over the years, the proper post being available now.

BTW, threading on such machines involves changing a couple of gears sometimes. Imperial threads are available when the 127 tooth gear is in place. Threading is otherwise a piece of cake, just make very light passes.

.


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## stupoty (May 4, 2022)

better-lathe-than-never said:


> Yes - I have about 12'' steel rod I can test the die on as well as a steel plate that I can use to test the tap on.  Realistically, I'm not going to learn single threading and then do that accurately on a new stud - it's too much too soon.



A chamfer at the start help and the rod should be a little undersized.

There are standard fit class's for threads that give you an idea of the tolerances, someone might have a chart 

Stu


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## better-lathe-than-never (May 4, 2022)

Well, my first attempt tonight went like this:

First, I took a flat 2''x2''x1/2'' steel plate which was already threaded to 9/16'' 18tpi just like my base; I re-drilled it and re-tapped it to the new dimension:  5/8'' 18tpi - that worked well, the new threads looked solid.  This was a practice run for re-drilling and re-tapping the compound slide's base to a larger diameter and it worked well using my drill press to keep the work and the tap perpendicular.

I then tried to make a new post out of some mystery steel I had on hand.   I turned one end down to .616x'', gave it a generous chamfer, mounted the drill chuck in the tail stock and pressed against the die handle all while spinning the lathe chuck by hand and maintaining pressure with the ram against the face of the die.   I had trouble keeping the die handle going straight.  Even with the ram pushing against the face it wandered around and produced somewhat 'wavy' threads which I wasn't happy with.  The new post fit in the threaded hole OK, but it wobbled off center axis as I threaded it down in place - all in all the quality of the new post was not good.  This try failed.   I have to decide where to take it from here:  use another type of material, and either buy a better die (chipped one of the teeth on my die) or wait until I'm able to learn single threading and do it all on the lathe.

The one good thing is that my old post is still holding up well through all this.


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## woodchucker (May 4, 2022)

better-lathe-than-never said:


> Well, my first attempt tonight went like this:
> 
> First, I took a flat 2''x2''x1/2'' steel plate which was already threaded to 9/16'' 18tpi just like my base; I re-drilled it and re-tapped it to the new dimension:  5/8'' 18tpi - that worked well, the new threads looked solid.  This was a practice run for re-drilling and re-tapping the compound slide's base to a larger diameter and it worked well using my drill press to keep the work and the tap perpendicular.
> 
> ...


not unusual. 3/8 and above start getting hard to thread with a die.  That's why I single point larger threads. I will chase it with a die if necessary.
The die will usually refine a larger thread quickly once single threaded to 75%-80% of thread depth.


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## ttabbal (May 4, 2022)

Looks like that lathe has a gearbox. I bet you could single point on it pretty quick. If you're new, skip all the stuff with the compound, set the tool at 90 degrees to the work, and take light cuts using the cross slide. If you're worried about timing, do it like a metric/imperial crossover. Take a pass, stop the lathe, back the tool away from the work, run in reverse to get back to the start and do it again. Do not disengage the half-nuts. If you can do that to get even half depth, the die will be a lot easier to run down the thread. 

If you're really stuck, post some dimensions and I'll make you one.


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## better-lathe-than-never (May 4, 2022)

ttabbal said:


> If you're really stuck, post some dimensions and I'll make you one.


It will take me a long time to start threading on this machine....  yes, the machine is capable of doing it - but I don't know anything about the threading chart on the face of the gearbox, or what gear arrangement to use or how to control the speed with the belts.  Plus the half nut on the timing dial is jammed (won't go down).  I do have some thread cutting bits that dad left me but that's about all the assets in this category.  Appreciate the info and support, but don't wait around - it may be a long while.


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## Larry$ (May 4, 2022)

better-lathe-than-never said:


> Plus the half nut on the timing dial is jammed (won't go down).


Time to take it apart and see why. Operation of half nuts is pretty simple, you will be able to fix most anything if you have a mill & a lathe. Might need to buy a part or two. Being able to thread on a lathe opens up a lot more of it's capabilities. Just another challenge that will broaden your abilities.


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## woodchucker (May 4, 2022)

better-lathe-than-never said:


> It will take me a long time to start threading on this machine....  yes, the machine is capable of doing it - but I don't know anything about the threading chart on the face of the gearbox, or what gear arrangement to use or how to control the speed with the belts.  Plus the half nut on the timing dial is jammed (won't go down).  I do have some thread cutting bits that dad left me but that's about all the assets in this category.  Appreciate the info and support, but don't wait around - it may be a long while.


the half nuts might not engage because of a lockout ... when you have the fine feed mechanism for turning set, it locks out the half nuts usually.


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## better-lathe-than-never (May 4, 2022)

woodchucker said:


> the half nuts might not engage because of a lockout ... when you have the fine feed mechanism for turning set, it locks out the half nuts usually.


Don't over analyze it - it stopped working when I accidentally rammed the tool into the spinning chuck...  I'm firmly in the destructive stage of the learning curve...  Need to take it apart and examine the damage...


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## better-lathe-than-never (May 5, 2022)

Was able to fix the half-nut for threading and got the timing dial working also.  Small victories, I guess.


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## better-lathe-than-never (May 16, 2022)

After many days of studying threading hieroglyphics charts, reconfiguring gears, grinding teeth and breaking belts, and other gymnastics I finally managed to build my new tool post.   Thx to many of you who helped this rookie through this sometimes difficult journey.  I will now re-tap my compound and maybe make a quick-release handle for it, now that I'm on a roll.


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## better-lathe-than-never (May 16, 2022)

Should I case-harden the threads especially at the upper end where it will be threaded/unthreaded the most?  The material used was 12L14 cold drawn steel.


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## stupoty (May 17, 2022)

better-lathe-than-never said:


> Should I case-harden the threads especially at the upper end where it will be threaded/unthreaded the most?  The material used was 12L14 cold drawn steel.



Should be fine as is.  

Stu


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## dewbane (Aug 21, 2022)

It was fun seeing someone work through the same problem I had. Your solution was a lot cheaper than mine! I solved the problem with the worthless M8 threads by talking myself into buying a real Aloris tool post, and tapping my compound for the 9/16" stud. I mean, problem solved, but that wasn't a very practical decision.


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