Lathe tool rest arm cracked

[DLB]

As an owner with warranty, I think you should gently complain to SS about this. These parts may have an unreasonably high break rate that can only be addressed through a minor design change. They may not be willing to address the issue, but IMO it is widely known that this is a weak link. But does SS even know about it? At a minimum, SS or someone else could offer an upgraded 510/520 tool rest.

The Greenie tool rest is of stouter construction and does not have that hole. I don't like the threaded mounting post because it takes a lot of tightening of the carriage height lock to prevent rotation. But also recognize that these have been in use for nearly 70 years so perhaps that is a minor complaint. That MGR video mentions grinding a flat into the post which will limit rotation, but I don't think that is workable because the upper joint between mounting post and arm does not rotate like all later versions. So in my mind rotation at the carriage is necessary to set the thing up. This version is also ~1.5" shorter than the 510/520/M7 version from mounting post hole to tool rest hole, a possible issue for small diameter turning unless one also has a 500 carriage.

I don't think we got a clear answer on whether the later 500 version has the offending hole. It is likely also about 1.5" shorter like the Greenie, but has the better post. It might be the best compromise solution for the OP, assuming it does not include that hole. I don't have one to look at.

From JPG's response I think adapting the cast iron arm from a Model 10 would require some form of metal work that isn't for everyone. And it also likely won't support small diameter turnings.

Ultimately if you find you like turning the best off the shelf solution is the Universal Tool Rest. Also the most expensive.

- David

[rogersk]

Here's a photo of my Model 500 tool rest from another angle. No hole.

[adrianpglover]

So I found this one on ebay, that has a full threaded post. I hadn't seen that before and wanted to ask about it. Does this come from a much older Mark V? Most of the posts that I see only have partial threads down one side. Seems to me like full threads would allow it to spin in the holder much easier.

s-l1600.jpg (226.6 KiB) Viewed 32763 times

[JPG]

Yes that is a Mark 5 version. Those 'grooves' are actually threads.

Yes it 'spins' in the carriage bore(too easily for some folks).

Note the absence of the 'lower' set screw that is required with the later gear rack version to allow rotation.

[chapmanruss]

There have been some questions brought up here.

Something to know is the 8" Lathe Tool Rest itself has remained pretty much the same going back to the Model 10E. At first there was a two-piece 8" Lathe Tool Rest for the very first Model 10E's made but are rarely found. Any era 8" Lathe Tool Rest itself can work in any era Shopsmith Model 10 or Mark Model.

The Post and matching hole in the Arm for the Model 10E & 10ER is a different diameter than the different models of the Mark 5/V's Posts and Arms. The Model 10's Post is smooth and 1" in diameter. I wondered is it possible to put the Model 10 post inside of the Mark's post to use the Model 10's Arm. Answer, it is not without some machining to either reduce the diameter of the Model 10's post to go into a Mark's post or bore out the Mark's post to match the diameter of the Model 10's post. Either way using the Mark's Post as a sleeve over the Model 10's Post.

Not all Mark 5/V posts and arms are the same. As mentioned, the first Mark 5 posts were actually threaded and originally attached permanently to the arm. Later that was changed to having a set screw hold the arm to the threaded post as is still used today. The Arm for the original Table System Mark 5 and Mark V 500 is shorter than the one for the other Mark V models with the larger Table/Fence Systems. The Model 10's Arm is also shorter than the damaged Mark V Arm shown. The Mark 5/V 500 Arm has the set screw hole in the same place for locking the Tool Rest in position as the later Mark Models Arm but did not have the hole where the crack occurred. Since they were able to drill and tap the hole in the Mark 5/V 500 arm why is that extra hole even there in the later Mark model's Arm? A question for the engineers.

The Carriage of the Mark 5/V 500 "locks" the post differently than the Carriage of the other Mark V models.

When I refer to the "other" Mark V models I mean the 510/505 and 520 plus these parts are the same for the current Mark 7 and the Mark 4.

[gleno]

My guess would be overtightening with the ratchet handle, with a set screw in the ShopSmith Allen wrench you'll never get anywhere near as much torque as you can with the ratchet handle

[adrianpglover]

So it didn't crack from that. I was roughing out a 4x4 pine board, had a catch, and that's when the tool rest got really loose and I knew something was wrong. It wasn't so much the ratchet handle, but more the stress of the catch on roughing out. I guess if I had taken a smaller bite, used a sharper tool, or wood that didn't have a large pitch section in it then the crack wouldn't have happened. Still though, there doesn't seem to be much reason to have the side hole in the part where the stresses are the greatest.

[DLB]

I can't think of a plausible reason for the hole's existence unless it is used during manufacturing to complete (drill and thread) the threaded hole that is directly opposite. Not suggesting sensible or reasonable, just plausible. The hole is clearly not there for the user.

I mounted my Greenie (with the threaded style of post) tool rest assembly on my Mark 7 with its wider 510 and on carriage. The edge of the tool rest is about 1-5/8" from the center of rotation of the spindle. Using the Greenie post and arm with a later rest reduces this to about 1-1/2". I would expect a later 500 tool rest to give close to the same results. That's too much gap for small diameter turnings, I would want to modify it or use a 500 carriage with it. (Swapping out carriages is trivial on a Double Tilt machine, this wouldn't be a deal breaker for me.)

If I was going to buy the parts to use a pre-510 tool rest, I'd ask the Model 10 guys if I can use a Model 10 carriage and tool rest on a late model Mark, and if I would want to.

- David

[HopefulSSer]

I can't think of a plausible reason for the hole's existence unless it is used during manufacturing to complete (drill and thread) the threaded hole that is directly opposite. Not suggesting sensible or reasonable, just plausible. The hole is clearly not there for the user.

- David

I have no doubt that's why it's there -- necessary for their manufacturing process. Otherwise they'd need a very long drill and very long tap to drill & thread the hole.

[JPG]

Model 10 carriage will NOT fit on a Mark 5... Way tube spacing is closer on a 10.