Craftsman 12x36 Rebuild and Improvement

[aaronrumple]

With the lathe now all disassembled, it's time to start the rebuild. That means starting with a base. Like most of these lathes, this on spent most of its time mounted to a 2 x 12 from the lumber yard on a top of a home made cabinet. I hope to do a little better and address some of the shortcomings of this lathe.

I've sketched up concept that is still getting refined. It will be a UHPC (ultra high performance concrete) frame, topped with either a granite or quartz countertop remnant. The concrete frame will provide most of the rigidity and the countertop will give the lathe a nice flat surface that even has the possibility to be used for some layout. The coefficient of thermal expansion is very similar for the cast iron @ 10.8, reinforced concrete @ 9.8, granite @ ~8 . Quartz is higher at 12 with the plastic resins. But man made quartz is more consistently flat. The specifications for quartz are a flatness of 0.063" over a slab that is 36" x 48". Not a surface plate, but a darn flat surface by any standard. And if you measure most of these, they usually exceed this standard. Specifications for granite is supposed to be 1/8" over 10 ft, or 0.0125" per ft. But I think the natural variation of this makes this more difficult and the hand polishing done at the edges, I'm sure puts in more dips.

The concrete frame will act as a torsion tube and beam below the lathe bed. and inserts will be cast in for bolting everything down. The concrete will be cast on the back of the granite, but not permanently secured. any holes will just be thru holes and the granite will be leveled on the base with silicone adhesive and pins.. So if I want to redecorate or modify the top later, it could be removed.

The top will have a hole and sump cut below the headstock to collect all the fluids and swarf below the top. If I want to clean the gears and headstock, everything will just drain down and not run all over the bench. I may rout in a recess in the top around the lathe to collect cutting fluids separately. (Or just steal a cookie sheet from the kitchen.)

Still tinkering with what I'm going to do with the legs. This will be in the basement, so I may just use the foundation wall and some brackets as the support for the back edge and a couple of simple support legs on the front. Not sure yet if I want to go that direction. I have a good spot and doubt I'll ever want to push the thing around.

 

[cjtoombs]

I think you are barking up the wrong tree here. Doing this might make the bed stiffer, but the cross slide and compound are still pretty flimsy on this lathe. I have a 12 x 36 Craftsman (Atlas) commercial, with the 1/2" bed ways, probably the same as yours. Taking heavy cuts on large diameter parts will flex everything visibly down to the bed. Also, you will have a time keeping that setup from twisting the bed. I did my mount to my stand so that the tailstock end of the bed is free to twist so that the bed will straighten out, basicaly a 3 point mounting. The base that I used is 1/4" steel plate, because it's what I had on hand. That being said, for it's light weight, it can take respectable cuts in reasonably sized stock with carbide tools. It won't hold a candle to my Harbor Freight 13 x 40, but then again, it doesn't leak oil from every place that's supposed to hold oil either. Good luck.

 

[mickri]

I have no idea if your proposed bench will work or not. Concrete likes to crack. Are you going to include any rebar or mesh to keep the concrete from cracking from the vibration of the lathe? Looks like overkill to me.

The manual for a Craftsman 12x36 on page 6 has a design for the stand for the lathe. It is made out of wood. Quartz and granite counter tops are rather thin and prone to cracking from point loadings. Might want to consider a different material for the top.



Do a search on the forum and you will get lots of ideas for making a lathe bench. Have fun with your project,

 

[aaronrumple]

I'm not super concerned about taking deep cuts. I'm doing small steel, some TI and carbon fiber. A lot of this is for setting up some tooling in relation to the lathe that would even be outside the realm of a much lager lathe. Hence the extra flat area to work with.

The design of the 101.28910 has issue starting right at the feet. They look rather elegant, but the load path isn't what it should be. Earlier models had 3 bolts but also had pads at the back to give it 4(5) mounting points. The back bolt between the two pads is along the center of the bed, so any twist and stretch of this bolt will lift the bed off the pad. You compare that to the SB 9 which has a simple block with 4 bolts on the corners for the bed and two at the base for leveling. The bed has a much more solid connection to the foot and then the base or table.


My '73 has even a more questionable design. The two bed bolts are way, way out on a cantilever. And then the two pads at the back are gone - just the one bolt hole. The cantilevers can flex and vibrate and the back bolt is just along for the ride. I'm guessing your concept matches the original thinking in that it would straighten out since these were mostly used on wood benches. The headstock 'foot' isn't much better.

I think the bed mounting could be improved if they had just done 4 simple holes. One could probably make that modification if you wanted to tap a couple of extra holes in the bed. I'm not interested in going to that extreme.



Yes, it won't ever be like the 16" x 8' I once had access to. But then again, I'm a lot less likely to kill myself. And I still think there is a lot of room for improvement working with the existing design. Just like my MG that had 90hp on a good day (maybe) and now 50 years latter is at 135hp.

 

[aaronrumple]

UHPC isn't what you know as concrete (I'm an architect.) It can exceed 29,000 psi and is ductile. It is reasonably new (as far as architecture goes) and is being used for some ultra high rise construction. They are even experimenting with it as a replacement for cast iron in milling and machining equipment. Especially for really big and custom stuff. Even the DIY CNC guys have jumped on the material for projects.


Check this video out:
UHPC Concrete

Thin slab granite can crack from imperfections, thermal shock and impact. I've spent my fair share of time dealing with poor granite installation in restaurant design. The quartz does much better. Rarely cracks and is much better at impact. And properly supported, neither will crack.

You can have a group jump up and down on this UHPC bench and it won't crack. Yes - that top is 100% concrete.

I have no idea if your proposed bench will work or not. Concrete likes to crack. Are you going to include any rebar or mesh to keep the concrete from cracking from the vibration of the lathe? Looks like overkill to me.

The manual for a Craftsman 12x36 on page 6 has a design for the stand for the lathe. It is made out of wood. Quartz and granite counter tops are rather thin and prone to cracking from point loadings. Might want to consider a different material for the top.

Do a search on the forum and you will get lots of ideas for making a lathe bench. Have fun with your project,

 

[aaronrumple]

Clean up of the lead screw was a bit of a chore. About half the screw was packed solid with dried up grease and sawdust. The other half was solid sawdust and wood glue. Waterproof glue of course. But it looks like both of those were good protection for the last half decade.