Bench Tube Construction

[DLB]

I received a very interesting email from Shopsmith customer service. They say that both the new bench tubes and way tubes are .050 thk but that they are made out of stainless steel. I can tell you that the bench tubes I received are magnetic but not as magnetic as my original tubes. Maybe they are made from a 400 series stainless like might be used in engine exhaust systems. I am still concerned about the thinner walls and increased deflection although this is my first Shopsmith so I'm not sure how much the thinner wall tubing might affect the machine in actual operation. I know there are folks on this forum with many years of Shopsmith experience so I would be interested in your opinion on the deflection issue.

If you are having reservations (I would) about using those you bought and/or buying way tubes you might try going through CS to see if they will set up a call for you to talk to engineering about the change. These calls are normally free for warranty/return type issues. I'm sure there was some analysis, and possibly testing, done before making the change.

I only know of one other forum member that likely has the new tubes. He is in cold country, and may not be using his machine. But from pics he posted I think KCollins has the same bench tubes on his shiny new Mark 7: viewtopic.php?p=292265#p292265

IIWM regarding the bench tubes I'd be more concerned about weight than rigidity. Weight helps stabilize the bench, especially in DP or vertical modes, and generally dampens vibration. I don't think there is normally a lot of stress on the bench tubes. Perhaps an ME among us can address this.

For way tubes I'd be concerned about everything. Do they resist the crushing force from headstock and carriage locks? Do they increase vibration? Does the reduced weight cause problems for lift assist? Do they flex under normal loads?

IMO the Mark has some undesirable flex, but whether any of it is attributed to the bench or way tubes and whether it would be worse with these tubes I don't know. The tendency of the main table to move under load is well known and documented. Something is deflecting under load. I would want to know if/how these tubes change that.

This change isn't for me, though I like the polished stainless steel part. If you decide the new tubes aren't for you I have some nice ones I could part with. PM me. Maybe someone closer also has a set, I'm near Fort Worth.

- David

[DavidMcM]

David,

Thank you for your detailed information and recommendations. I had not seen the post from KCollins. His bench tubes look like the same ones they sent me. I happen to be a mechanical engineer by day which is why I asked the question about deflection. There will certainly be some weight reduction but I am much more concerned about deflection and the overall rigidity of the machine due to the significantly thinner wall thickness. When I get some time, I will run some calcs. The change to stainless steel is certainly an improvement from a corrosion standpoint.

[BuckeyeDennis]

David,

Thank you for your detailed information and recommendations. I had not seen the post from KCollins. His bench tubes look like the same ones they sent me. I happen to be a mechanical engineer by day which is why I asked the question about deflection. There will certainly be some weight reduction but I am much more concerned about deflection and the overall rigidity of the machine due to the significantly thinner wall thickness. When I get some time, I will run some calcs. The change to stainless steel is certainly an improvement from a corrosion standpoint.

Cool, we need a good ME on this forum!

My personal experience is that that my 2005-vintage tubes are more than adequate for most operations. But they leave a lot (of mass, damping, and rigidity) to be desired when turning large bowls. I have to take it really slow and easy with those, even using a speed reducer. I’m hopeful that the 1/4” wall thickness of my 10ER tubes will offer a substantial improvement, once I get that machine in service. But I fear that the new 0.050” way-tube walls will render new machines all but useless for lathe turning anything other than spindles or pens.

[SteveMaryland]

Continuing with the idea of fixing the new Shopsmith tubes, it appears that 7 pieces of Schedule 40 or 80 1/4" pipe will fit into a 1.75 OD, 0.050" wall tube as shown in the attachment. Not a zero-clearance fit but wrapping the pipes with ductape could remedy that.

Steel pipes stuffed into the tubes certainly would increase stiffness. The added weight would be a plus in some applications. Machine damping could be improved by filling each pipe with something like asphalt or pearlite-plaster (structo-lite). This 7-pipe arrangement could be installed without pulling out those new end bushings - 6 pipes go in first and then the seventh goes in the middle.

Additional 9 pipe configuration attached. This combination is an exact fit with the tube ID.

So who is going to be the beta tester of this??

[thunderbirdbat]

You could fill the tubes with sand. Ship propeller shafts are filled with sand or at least they used to be.

[BuckeyeDennis]

I’ve contemplated filling my SS tubes with epoxy granite. I once researched the stuff when working in the machine tool industry, and it has damping characteristics that are superior to cast iron. It’s an aggregate similar to concrete, except that the fill is granite rather than limestone, and the binder is epoxy rather than portland cement.

https://en.wikipedia.org/wiki/Epoxy_granite

I’m not sure where one could buy it in small quantities, but I see that there are now a number of blogs and videos on how to make it yourself.

[SteveMaryland]

The ideal remedy would be one which was easily installable, had high flexural stiffness, super damping, high density, AND could be removed from the tubes (for shipping). Sand has some of those properties and might also increase stiffness if hard-packed inside the tube. Not sure.

Certain gravels have high intergranular friction, maybe they could be poured in dry and would dry-lock without need for the epoxy.

Flexural stiffness is most needed in the way tubes. So maybe do sand/gravel in the bench tubes, and steel pipes in the way tubes. Problem solved?

BTW, I have seen the epoxy/granite in countertops. They look terrific, but a Geiger counter will go crazy near them. Lots of radioactivity in granite. If people only knew that about their nice new granite countertops...

[DLB]

The ideal remedy would be one which was easily installable, had high flexural stiffness, super damping, high density, AND could be removed from the tubes (for shipping). Sand has some of those properties and might also increase stiffness if hard-packed inside the tube. Not sure.

Certain gravels have high intergranular friction, maybe they could be poured in dry and would dry-lock without need for the epoxy.

Flexural stiffness is most needed in the way tubes. So maybe do sand/gravel in the bench tubes, and steel pipes in the way tubes. Problem solved?

BTW, I have seen the epoxy/granite in countertops. They look terrific, but a Geiger counter will go crazy near them. Lots of radioactivity in granite. If people only knew that about their nice new granite countertops...

Total mass of the way tubes could be problematic, especially for PowerPro owners, when rotating the way tubes vertical. For the way tubes, I think the mass of the way tubes would need to be reasonably close to the baseline with 0.120" walls. IIRC PowerPro adds about nine pounds, very noticeable at any useful headstock location. Seems to me that adding that much steel pipe might add too much mass, but I didn't run the numbers. I like the pipe inserts for bench tubes. I was thinking the curing time for an epoxy inside the tubes might be really long.

I remain somewhat skeptical that SS changed the way tubes to 50 thou walls. It would not be the first time that information attributed to SS Customer Service was later found to be incorrect. Seems like an idea so bad that it couldn't be true, but this wouldn't be a first either.

- David

[rpd]

By the time you have bought that many EMT, or that much epoxy, would it not be cheaper, and easier, to just buy a set of vintage tubes, or new DOM tubing with thicker walls.

[RFGuy]

By the time you have bought that many EMT, or that much epoxy, would it not be cheaper, and easier, to just buy a set of vintage tubes, or new DOM tubing with thicker walls.

+1
I was thinking the same thing...