DIY Epoxy Granite Lathe #3: Linear rails!

[@RotarySMP]

Nice progress. Spread the bed rails to the max width the bed casting allows. This will reduce the forces on the Hiwin trucks, and increase stiffness. You can make the saddle rigid enough to resist the mending moment, but if would space the rail closer, you are wasting a lot of the stiffness inherent in the bed casting. In commercial machines, a step gets machined so the rail has a reference should to align it. Rails are pretty flexible as is. Dont worry about motors sticking out.

[@robertsteinwandel6658]

That honestly makes a lot of sense, I was thinking of ways to minimize the saddle deflection in the center and I think I stopped considering which parts are easy to stiffen and which aren’t. I had seen that actually! The Hiwin guide has a section on straightening the rails with a bunch of options and great visuals. Unfortunately for me I don’t think the ridge is very feasible. I have no mill to cut the ridge in, and the only other way to make one I could think of is taking a strip of steel with a very straight edge and using metal epoxy to glue it down to the insert. Im not sure that would work though, so that brings me to using an indicator and a straightedge to run the indicator back and forth until my rails are straight and tightening the bolts as I go. Seems like a huge pain but Hiwin said it’s possible? If you’ve got any other ideas Im all ears hahaha Thanks again!

[@RotarySMP]

@@robertsteinwandel6658 That is a good solution for a one off. It would be tough to scrape around a step like that.

[@bobweiram6321]

For one, you could clamp the drill guide to the bed after centering the bit. By the way, it is also an excellent tapping tool for getting a nice clean and straight tapped hole.

[@robertsteinwandel6658]

Thats a great idea, thanks!!

[@MyDabblings]

You mentioned trying to get the linear rail in position as good as possible with your caliper. You might find that easier if you used the other end of your caliper as it has large contact points.

[@robertsteinwandel6658]

Honestly thats a way better idea, I think I was just needed to take a second to think what I was doing for the part hahaha

[@edwardortman2593]

I am thinking of building like this as well for my next bigger lathe. I wanted to avoid the leveling/flattening issues... last night when I probably should have been sleeping I spent about 8 hours thinking over how one could make a better surface that was more easily flattened to a perfect surface. It seemed that most any ordinary metal will have issues with being out a few thousands of an inch no matter what you do and you would be stuck with trying to grind them down to the lowest points. Potentially a lot of work. Next I though about avoiding metal and just going with the poured surface though that would also be impossible to get perfect and you would be removing material to the lowest point and "trying" to do that in a way that maintains a perfect surface. Again a lot of work.. I have not come up with a way to create a perfect surface, heck I tried to do that when I poured the concrete pad for my sawmill, it seemed just about perfect until I put my rails on and started bolting them down and checking the heights across them and I was out by up to a 16'th of an inch all over the place. I had to just live with a lot of it as the more I tried to flatten everything out it would throw the rail out more in other areas. I got to thinking about maybe instead of going for a perfect surface from the gitgo coming up with a way to make it physically easier to work the surface to "make it" perfect. Maybe a slightly raised set of lines across the poured surface that would be physically easier and less time consuming to tool down to a perfect surface? Any thoughts?

[@robertsteinwandel6658]

You have a really cool line of thinking here, I spent a ton of time trying to avoid the process and ended up just caving and doing it haha. So I like your idea with the poured surface, although if you use linear rails you need something to bolt down to. They do make a self leveling epoxy which has had mixed results for people. So you could put self leveling epoxy over your steel youd bolt your rails to, and theoretically the surface would be flat to the same curvature as the earth (.008in per foot I think) this is pretty good, and it would be consistent so maybe you could account for it with shims or something to avoid any flattening. If I went back and did it all again, I would have gotten 1 solid sheet of 1/2in steel for the entire top of my base casting, to bolt everything to. JB weld 1/16th in steel strips under the rails to raise them up, then just grind that flat. It would’ve reduced the surface area I had to grind by like 80% and having the whole top be 1/2in steel is much easier to work off of than 3 steel inserts which might not be coplanar and have gaps of EG between them. I do like the idea of lines to reduce surface area to flatten, although I hope that reducing the surface area the linear rails rest on wouldn’t make them any less rigid What do you think?

[@edwardortman2593]

@@robertsteinwandel6658 I was thinking threaded metal under my poured surface with something like wax or rubber plugs to keep everything out of the holes and threads. Under the rails after flattening the surface I figured use something like bondo which would fill in the low areas of the ridges left for a flatter smoother surface. Bondo is nice and soft so any excess can easily and quickly be sanded back down to the flattened surface. I was thinking of using the three plate method of trueing a surface using finished granite stone to work down the concrete. I can get very flat finished granite in the form of cutting boards, glue some sand paper to that and I should goof true sanding plate. I also realized after a great deal of though that the height axis is not so important, if it is off a couple three thousands there would be no real issue. it is the side to side axis that is of the greatest importance on a lathe. I was thinking get the mounting platform not perfect but good and then fine tuning the rail system might be the more efficient for me way to go. I was also thinking I might go three rails instead of two. Having a center rail inline with the lathe head seems potentially stouter and less likely to create flex in a rail in the first place. That would also put the two outer rails further out which would reduce the effect of being out slightly in height by the it simply being further away from the centerline of the lathe head. New to all of this so I am still thinking it all through yet.

[@ShopperPlug]

Yes, it will give you issues due to slight thermal differences, you said on your previous video that you got it flat down to 1/2 a thou, thats near 12 micron precision. I know that professionals who scrapes need to do this type of work in a professional environment with temperature controlled room, they also wear special heat shielded apron while scraping since the body's temperature will radiate to the granite or thing that is being scraped and throw off micron level readings.

[@robertsteinwandel6658]

Hmm interesting Well at some point Ill have to get it to a temp controlled environment, not an option for now though unfortunately

[@ShopperPlug]

@@robertsteinwandel6658 It great that you made videos on making it and showing what issues might rise. Thanks.

[@robertsteinwandel6658]

@@ShopperPlug Thanks! It’s funny, actually building the lathe has shown me so many issues or better ways to do things, once I finish it I almost want to just start on another lathe hahaha. It would go so much more smoothly after already doing it once lol

[@zJericho101z]

Awesome!

[@robertsteinwandel6658]

Thanks! The videos get better as they go along I swear hahaha

[@IainMcClatchie]

I was spitballing the idea of running 3/16" brake line all through my epoxy granite base, and circulating water through it with a thermoelectric element driving it to constant temperature. But I thought, why do I keep making things so complicated? Now it seems a lot less like overengineering.

[@robertsteinwandel6658]

Interesting thought, although you can also stop the banana effect by epoxying another bar of steel to the bottom, or by using threaded rods and a plate, and putting some tension on it, which may be easier/cheaper

[@Nebulorum]

There are magnetic drill presses, maybe you could rent one. Also AFAIK steel drilling should be slow and steadily.

[@robertsteinwandel6658]

Absolutely yes, it should be slow. A mag drill would definitely be the way to go you’re right, I totally forgot about that. I don’t own one and can’t afford one so for just a few minutes worth of work it’s probably not worth it, but thats a great point. A mag drill would actually be a really fun project after the lathe is done hahaha- might think about that for later

[@TheIntermont]

Screw some MDF to the drill stand, then glue some magnets to the bottom.

[@nickp4793]

Hi, curious if the warping due to temperature change was proven 100% since you made this video. Did you check it again when the base was at another temperature? If so, did it return to flat?

[@robertsteinwandel6658]

It does, I think its ~73 degrees that its flat, above or below that and it starts to banana I may try to bond a piece of steel to the bottom to see if having the strain on both sides will stop it from bowing, hut I haven’t yet

[@nickp4793]

@@robertsteinwandel6658 Ok, thanks for the follow up. My design is symmetrical. EG inside a 6" square alum extrusion. I suppose it would stay straight during thermal changes, but that's an educated guess at this point.

[@robertsteinwandel6658]

Nick P shoot I didn’t see you responded, sorry! Actually I remember from your video haha, yeah I think that should be fine, the only thing that could mess it up may be the rails (forget if you were doing standard ways or linear rails) but those would give you some asymmetry. If its stored insode though shouldn’t be a problem at all Im thinkin (hopefully lol)

[@taddmooney3575]

I love that tap handle. Where did you get such a tool, or did you make that yourself?

[@taddmooney3575]

Just answered my own question reverse image searching a screenshot. Looks like it is from a Gearwrench tap and die set.

[@robertsteinwandel6658]

@@taddmooney3575 Thanks haha, mines actually an Irwin one I got in a pack of like 5taps at lowes. Got it maybe 5 years ago but Id assume they still make it. Honestly great tap wrench, it’s really surprisingly nice for the like 30$ set it was in

[@ryteulopki8069]

Very loud music over your quiet voice is terrifying !!