# Through the Spindle Lathe Chuck Stop for PM 1340GT



## mksj (Oct 22, 2017)

I have always found lathe chuck and collet stops somewhat lacking and difficult to use, especially with 5C and ER collet chucks. The 5C stop that I previously used, screwed into the back of the collet and stop slide mechanism was a piece of round stock held in place with an Allan set screw. So no fine (vernier) adjust and no way to set it relative to the spindle with the collet in the chuck. Depending on how hard the 5C collet was pulled in, it would change the distance relative to the spindle. I recently made an ER40 lathe collet chuck, and have not seen any chuck stop systems for it either. I have seen one through the spindle chuck stop made by Accu-Stop, but kind of clunky in that it uses an expanding mandrel spindle lock as has no fine vernier adjustment once it is locked. It also costs over $400, I think I will pass on that one.

I wanted to design a stop system that could be used in various capacities with different chucks, that would have both a course and fine stop adjust, and would fit a wide range of diameter stock. Since I use a spindle spider, I figured I could use the spider bolts to lock the body of the stop in place, and then use a fine pitch threaded rod for the vernier adjust.  My spindle internal diameter on my PM 1340GT measures 1.59", so I chose some 1.75" x 7" 6061 for the stop body, I turned most of the length down to the spindle diameter except for an end flange (~3/4") and knurled the flange.  I then center bored the stop body with an 11/16 drill, and drilled a 3/4" hole to 5". I then internally threaded the  11/16" bored end to 3/4"-20 UNEF. Once threaded,  I parted off 1/2" of the flange to create a flange lock ring. I chamfer both the edges before parting it off. The stop body  was then put in an indexer and I milled four channels at 90 degree intervals, each one 0.25" wide by 0.075" deep. These channels line up with the spider bolt holes, the brass tips of the spider bolts slide in these channels so the slot's length set the sliding limit and any deformation form tightening  the spider bolts is in the channels not on the body.

The stop bar  is 3/4" 6061 round stock, in the raw form it is somewhat irregular and the diameter was closer to 0.755". I turned the bar down to 0.749" and then cut a 3/4"-20 male thread about 7" on one end, the other end was tapped with a 1/4" female thread to accept various sized screw in steel tip stops.  A cap is needed for the end of the threaded bar to be able to turn the bar for the fine verneir adjustment. The cap is 1" 6061 rod, knurled 1", center drilled the bar stock with a 11/16 drill to 1/2", and then blind threaded the female thread in the cap. Since I use the proximity stop system, I use the internal thread cutter to cut an ending grove within 0.001" of the cap wall, then proceeded to cut the thread.   The major diameter is ~0.75, the minor ~0.69, so several passes at 0.01" with a total depth of just over 0.06". I use the cross slide for setting the cutter depth, so the stop position remains the same. Pretty much pushing my internal threading bar insert to its maximum thread depth limit. I did order a 3/4"-20 tap, but at the end of the day I didn't need it. Might have been handy when cutting the 2" 3/4"-20 internal thread on the stop body, this was also at the maximum length of my internal threading bar.

Since the stop bar is supported on the spider end but not the chuck end, you need to add a support ring for the bar that sits at the chuck end. So turned some 6061 ring so it has an OD of 1.59", ID 3/4" and width of 1" chamfered the edges so it slides smoothly into the spindle. I use a set screw to hold it in place, the position is set so that the ring face is even with the end of the headstock spindle with the stop at its maximum stop extension at the chuck end. Steel stop tips were cut from drill rod turned to an OD of 0.749", then two smaller diameter extensions are 0.499"x1.5" and 0.249"x1.5". I turned the diameters slightly under as to not interfere with the clamping of 0.500" or 0.250" stock. Other size tips can also be fabricated.  At a later date I plan to make some precession height plates that will fit between the chuck jaws and will be held in place by drawing back on the chuck stop bar which will hold the plate against the face of the chuck body. Royal sells a set of three of these for $300, a bit crazy.

Anyway, the stop bar slides into the chuck body and then is threaded through the remaining 1.5", the flange lock ring is then screwed on and finally the rod end cap. It stays locked in place, but at some point I may consider using a left hand Allan screw in the cap end to lock it on.  Screw in the desired tip, slide it into the spider end so the grooved reliefs align with the spider bolt tips.  I have a little over 4" of course adjustment in the spider and another 5" from the threaded bar. The tips also can be adjusted, so the 3/4" one is 0.500", the smaller ones are 1.75" from the rod end. Different length stop bars can also be used. The repeatability on my 5C collet holder is under 0.001", so that is good enough for me.

Stop rod with thread inserts, stop body, rod locking ring, stop rod end cap and spindle guide bushing for rod.






Assembled, ready to slide into the spindle.



Inserted and aligned with spider bolts. Fully extended into the spindle.




Fully retracted position, the stop body movement is limited by the milled channels in the body, about 3" remains in the spindle.



Stop in 3J chuck and the 5C chuck.




Cutting internal and external threads using a proximity stop system on a PM 1340GT lathe. Each thread cutting pass is 0.01" depth, the thread is a 3/4 - 20:


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## Bamban (Oct 22, 2017)

Nicely done,  Mark.


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## Alan H. (Oct 22, 2017)

Great concept Mark and nicely executed.  You have included the details so others (especially me) can replicate this good idea!

You always share you good ideas and I am sure others appreciate it as much as I do.
Thanks


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## Firestopper (Oct 23, 2017)

Nice Mark, gonna steal that idea for sure.


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## mksj (Oct 23, 2017)

Thank you for the comments. A few suggestions for others they may be interested in making a similar lathe chuck stop system, probably easier for many to just get a 3/4-20 plug tap for the internal threads. I picked up one for $18 shipped, but never used it. Normally I do not like aluminum to aluminum threads, they can gall easily if not well lubricated. In this case, probably not a big issue, but one could press in a bearing bronze threaded bushing into the stop body. You may need to adjust some of the clearances/tolerances  to suit your individual lathe, so just a starting point for ideas. Others always improve on the design.


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## Firestopper (Oct 23, 2017)

Great work as usual brother.
You could always use a dab of anti-seize on the aluminum threads.


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## KMoffett (Oct 24, 2017)

I've been thinking of posting this for awhile, and it seems like this might work here. So, here is another "stopper".

I was looking for a way to make a thru-spindle stop for my JET lathe.  Something easy to install and remove, and easy to adjust.  I thought the design of expandable mandrels seemed to be a workable solution. I happened across Harbor Freight 's exhaust pipe expanders that would fit my spindle bore. They became the basis for my design.

Two Harbor Freight Medium Tail Pipe Expanders #69548.
Twenty four inches of 1/8" steel pipe, threaded 8" of 7/16"-14 on each end.
Thirty inches of brass all-thread rod.
Two aluminum rounds 1" long. Both drilled #U 3/4" deep and tapped 7/16"-14. Also, one drilled #F through, and other drilled #7 through and tapped 1/4"-20.
Six 7/16"-14 nuts.
One 1/4"-20 wing nut.
One knob for 1/4" shaft .
Four #117 O-rings (as replacements).
One cheap 11/16" socket with the square bored out to 7/8".
One foot of 3/4" EMT.

Two 7/16 nuts each are threaded about 5" onto the 1/8" pipe from each end.
The expanders are slid onto the pipe with the hex recesses toward the center
One 7/16" nut fits into the recess of each expander. And the second ones are used as a jam nuts to prevent rotation.
Another 7/16" nut is threaded on to each end of the pipe and up against the expander.
The two aluminum rounds are threaded tightly on each end of the pipe.
The brass rod is slipped through the round with the clearance hole, down the pipe, and threaded through the other round.
The wing nut is threaded on the rod, on the end with the clearance hole.
The knob is fastened on the brass rod after the wing nut.
Braze the 11/16" socket to the end to the EMT

Adjust the positions of the expanders along the pipe so one is near each end of the spindle. Slide the assemble into the left end of the spindle so the right end expander it near the chuck. Use the socket pipe to tighten the nut and seat the right end expander.  Do the same on the left end expander. Screw the brass rod in or out to fix the stop position. Thread the wing nut down the rod to jam against the left round and lock the stop position.

Ken


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## JimDawson (Oct 24, 2017)

KMoffett said:


> I've been thinking of posting this for awhile, and it seems like this might work here. So, here is another "stopper".
> 
> I was looking for a way to make a thru-spindle stop for my JET lathe.  Something easy to install and remove, and easy to adjust.  I thought the design of expandable mandrels seemed to be a workable solution. I happened across Harbor Freight 's exhaust pipe expanders that would fit my spindle bore. They became the basis for my design.




Very inventive.  Nice job.


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## darkzero (Oct 24, 2017)

Nice work.



KMoffett said:


> I've been thinking of posting this for awhile, and it seems like this might work here. So, here is another "stopper".
> 
> I was looking for a way to make a thru-spindle stop for my JET lathe.  Something easy to install and remove, and easy to adjust.  I thought the design of expandable mandrels seemed to be a workable solution. I happened across Harbor Freight 's exhaust pipe expanders that would fit my spindle bore. They became the basis for my design.
> 
> ...



That's pretty clever. Kinda reminds me on how my Yuasa spindle work stop works.























Obviously I cheated by buying one. My salesguy at the local MSC gave me an additional discount off the sale price so I couldn't refuse. It was my birthday present to myself some years back. Stop rod unscrews on the Yuasa so I made me a few additional stops to accomodate my needs.


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## KMoffett (Oct 26, 2017)

Only problem I've had with my exhaust pip expander version, is the o-rings. The #117 Buna-N o-rings don't seem to like the circumferential stretching. After being in place for a long time they start to crack and come apart. Easy to replace (I had to buy a dozen). But someone might know of a better o-ring material...Silicon?, Viton?, Neoprene?....?

Ken


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## RJSakowski (Oct 26, 2017)

KMoffett said:


> Only problem I've had with my exhaust pip expander version, is the o-rings. The #117 Buna-N o-rings don't seem to like the circumferential stretching. After being in place for a long time they start to crack and come apart. Easy to replace (I had to buy a dozen). But someone might know of a better o-ring material...Silicon?, Viton?, Neoprene?....?
> 
> Ken


Try urethane


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## RJSakowski (Oct 26, 2017)

And here is my version of a work stop. http://www.hobby-machinist.com/threads/lathe-headstock-work-stop-g0602.32809/


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## 4GSR (Oct 26, 2017)

KMoffett said:


> Only problem I've had with my exhaust pip expander version, is the o-rings. The #117 Buna-N o-rings don't seem to like the circumferential stretching. After being in place for a long time they start to crack and come apart. Easy to replace (I had to buy a dozen). But someone might know of a better o-ring material...Silicon?, Viton?, Neoprene?....?
> 
> Ken


Look for some very small extension springs.  Leeco my have something in stock, or even McMaster-Carr, too. If I find something, I'll post it here.

Edit:  Here's one I found at McMaster-Carr, might be a little long but should work.
https://www.mcmaster.com/#9654K423

Or make your own with this https://www.mcmaster.com/#9664K42


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## KMoffett (Oct 27, 2017)

Thanks for the suggestion Ken.
But, in my design the rubber'ish o-rings are not only to hold the segments together, but mostly the source of the friction between the stop assembly and the spindle bore. The expander segments never touch the bore wall, unlike in their intended purpose in an exhaust pipe. I'm afraid springs would have less friction without crushing them, and might allow the assembly to slip. 

Ken


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## Robert LaLonde (Oct 27, 2017)

Very nice with the sliding spider mount.  I was a little concerned about brass on aluminum (galvanic corrosion) and aluminum in aluminum (galling), but if eveything is well oiled it should keep moisture (humidity) and air exposure of the surfaces to a minimum.  I'm a big fan of stainless in aluminum, but finding 1/2-20 precision stainless rod might be a trick.  I don't know.  I haven't looked. Very nicely executed.  

The tail pipe expander is a nice trick.  I have a few of them in my automotive specialty tools box.  I've never used them for anything except expanding tube.  McMaster has a pretty good selection of O-rings as does the O-Ring Store.  If you have a hydraulics supplier nearby like a "Parker Store" they will likely have Buna 75 and viton rings on hand locally.  Buna I beleive is slightly more reactive with air.  Viton is lerss tolerant of low temperatures.  I typically use Viton when tuning air guns as it tends to hold up better, but I live in the desert.  Low temps are not as common and when its that cold I tend to stay inside anyway.  It might be a good idea to look up a table of properties for various o-rings if you want to stay with them.  The idea of a small diameter tension spring is a good one of you kind find one the right size for the application.  Also very nicely executed.


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## 4GSR (Oct 27, 2017)

KMoffett said:


> Thanks for the suggestion Ken.
> But, in my design the rubber'ish o-rings are not only to hold the segments together, but mostly the source of the friction between the stop assembly and the spindle bore. The expander segments never touch the bore wall, unlike in their intended purpose in an exhaust pipe. I'm afraid springs would have less friction without crushing them, and might allow the assembly to slip.
> 
> Ken


You want the expander segments to touch the wall or bore of the spindle.  Believe me, the O-Rings will squish almost immediately with the smallest amount of force.  I think you will find that the segments or what I call "slips" are doing all of the grabbing in the bore.  The O-Rings are in there for the ride and holding the segments in place.  It will take a big piece of rubber to hole it in place.  
Ken


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## mksj (Oct 27, 2017)

Lots of great ideas, the mandrel systems are more adaptable to various spindle bores but can be a bit more time consuming installing if using nuts and some do not allow fine adjust once locked in. The Yuasa is very nice and simple, Rovi sells a similar expandable  stop for around $200. They do not come with different size tips to fit into collets, although they could be modified as such.  I probably have $15 in materials in the design I used, it is quick to set both course and fine adjust, and it is solid. It does require a spider and is specific to the machine bore, I would consider a single expanding mandrel system otherwise.  I have not had any issues with galling, I used some NLGI 2 bearing grease on the threads which seems to works fine.  I have used bronze as a bearing material on some projects, I used it in my aluminum machine handles as the bearing surface. A little fancier and smoother, but not really necessary in this setup. The fine adjust  threaded rod can be threaded in/out quickly by just running the lathe at a low speed and holding on to the stop rod end cap.

http://www.roviproducts.com/spindleworkstop.htm


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