Through the Spindle Lathe Chuck Stop for PM 1340GT

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
Click to expand...
Try urethane
 
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
Click to expand...
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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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
 
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.
 
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
Click to expand...
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
 
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
Rovi.jpg
 
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