Tool Rest Arm Rotation

algale · Post by **algale** » Thu Mar 17, 2011 7:12 am

I've been doing some lathe work on my 520 and encountering an irritating and dangerous situation. Under use, the arm (294) of the tool rest is rotating while I work. No matter how much I tighten the handle/set screw (296a) on the arm, the arm wants to twist or turn on top of the post (293) during use.

I should point out that because the work piece is about 6 inches long and 2 inches in diameter, the geometry of the carriage requires me to angle the tool rest arm in order to bring the tool rest itself close to the work piece. If you were to look down on top of the post and imagine the arm as the hour hand of a clock, the arm would be pointing to about the 2 o'clock position. The rotation is always slightly counter clockwise, bringing the arm and the far right end of the tool rest toward the work piece. The tool rest hasn't caught the work piece yet, but I've had a couple of heart-stopping near misses.

I removed the arm and checked to see if the screw end of the handle is making contact with the top of the post and it definitely is leaving a pretty good mark there. Still, it is rotating. I also checked to make sure the rotation isn't caused by a twisting of the post in the carriage and when the arm rotates the post definitely is not rotating in the carriage.

Anybody got a suggestion (other than buying a Universal Tool Rest?).

Alan

twoblocked · Post by **twoblocked** » Thu Mar 17, 2011 7:44 am

Alan:

I look forward to other responses on this.

I had a similar problem and partially solved it by filing all marks off of the post. But the lower end of the post does rotate in the carriage a ways. So when I set my tool rest arm, I bump it towards the work to it's limit and then set the rest itself where I want it, usually parallel to the work.

I don't think it is a really good design, but useable.

algale · Post by **algale** » Thu Mar 17, 2011 7:47 am

Interesting thought about filing marks off of the upper part of the post. I'll give that a try.

damagi · Post by **damagi** » Thu Mar 17, 2011 8:26 am

I asked mike (the shopsmith sales guy) about this when I saw him a few weeks ago. He said that you can try grinding flat spots such that it gets gripped better or go with the universal tool rest. for most things its not a problem, but I have hit the same issue and upgraded to the universal lathe tool rest as a result.

As a result of the tool rest movement I had a bowl explode on the lathe. Mine would rotate about 3 to 5 degrees in either direction.

foxtrapper · Post by **foxtrapper** » Thu Mar 17, 2011 9:27 am

Couple of ideas and thoughts.

Multiple lock screws better lock something onto a shaft.

If you will never adjust it on the shaft, use loctite or such.

Dimpled holes on the shaft to run the set screw(s) down into better hold a position, though they limit the number of positions.

Is the rotation actually of 294 on 293? Have you used a marker line to make absolutely sure? For 293 can wiggle in its base as well.

Should you be moving the rest instead? As in are you working beyond its stability range? Perhaps you need to adjust the rest more often.

Are you positioning the rest correctly to begin with? Too far away, too high or too low, all create torque, and you don't want torque.

A nut welded into the top of 293, a hole in the top of 294, and a bolt running through 294 into that nut welded in the top of 293. You can lock 293 in place solidly this way, and retain infinite adjustability.

pennview · Post by **pennview** » Thu Mar 17, 2011 9:55 am

As was already suggested, file off any burrs that are present on the upright. Also take a look at the setscrew; perhaps the face is damaged. I haven't looked at mine on the 510, but perhaps this is a case where you want one of those setscrews with a serrated end to better bite into the upright.

Also, the older variety upright was different in that the grooves used for raising and lowering it went completely around the shaft (like screw threads), whereas on the newer version the grooves are similar to the rack on the saw table uprights. With the older variety, you didn't need to loosen the setscrew connecting the upright with the horizontal arm because you could simply rotate the upright and arm simultaneously and then square your tool rest via setscrew with your turning. This still leave you with the possibility of the upright rotating and resulting in the same problem, but it has not been a problem for me using a model 500. I've not done much turning on the 510, so my experience with the newer upright is minimal.

algale · Post by **algale** » Thu Mar 17, 2011 10:15 am

damagi wrote:I asked mike (the shopsmith sales guy) about this when I saw him a few weeks ago. He said that you can try grinding flat spots such that it gets gripped better or go with the universal tool rest. for most things its not a problem, but I have hit the same issue and upgraded to the universal lathe tool rest as a result.

As a result of the tool rest movement I had a bowl explode on the lathe. Mine would rotate about 3 to 5 degrees in either direction.

YIKES! You sound fortunate not to have been injured. I hate to say it, but if Shopsmith knows this is an issue with the design of the tool rest they are really asking for another products liability suit someday.

algale · Post by **algale** » Thu Mar 17, 2011 10:17 am

[quote="pennview"]As was already suggested, file off any burrs that are present on the upright. Also take a look at the setscrew]

I tried using both a set screw and the handled screw that comes with the upgraded tool rest. Neither did the job. I am going to try filing off the burs and starting over.

algale · Post by **algale** » Thu Mar 17, 2011 10:36 am

foxtrapper wrote:Couple of ideas and thoughts.

Multiple lock screws better lock something onto a shaft.

Too bad it doesn't come that way! I dont have the tap (or is it a die) to put a threaded hole on their, but I might go get one.

foxtrapper wrote:If you will never adjust it on the shaft, use loctite or such.

Not practical. It does need to be adjusted because there's no one-size-fits-all position for the arm that will let the tool rest reach (or at least get close) to pieces of different diameters.

foxtrapper wrote:Dimpled holes on the shaft to run the set screw(s) down into better hold a position, though they limit the number of positions.

Hmm. What about a series of closely spaced through-holes, just large enough to accept the thread]Is the rotation actually of 294 on 293? Have you used a marker line to make absolutely sure? For 293 can wiggle in its base as well.[/QUOTE]

Rotation seems to be only on the 294.

foxtrapper wrote:Should you be moving the rest instead? As in are you working beyond its stability range? Perhaps you need to adjust the rest more often..

I don't know what the "stability range" is]Are you positioning the rest correctly to begin with? Too far away, too high or too low, all create torque, and you don't want torque.[/QUOTE]

Rest is within 1/4 inch and is mid point on the turning.

foxtrapper wrote:A nut welded into the top of 293, a hole in the top of 294, and a bolt running through 294 into that nut welded in the top of 293. You can lock 293 in place solidly this way, and retain infinite adjustability.

Interesting. Not sure that this would necessarily work since you still have a rotational force.

JPG · Post by **JPG** » Thu Mar 17, 2011 10:56 am

I cannot say I have ever encountered this problem. I have done lathe work solely on my Goldie. The older(500 like) machines have a shorter arm than the newer version. I have been using non-biting setscrews which do not have the scaring of the post the cupped or serrated ones have. Since the post can rotate(360) the post must be secured in the carriage.

Keep in mind there are two setscrews and the carriage clamp that can cause this. Both the arm and the rest can rotate(independantly).