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what diameter should support points be??

Slarti42uk

Plastic
Joined
Jun 20, 2017
Hi,

First time post here. I've recently bought a used surface plate and I'm in the process of making a wooden stand. The plate is granite, 25"x16"x4" about 180lbs (80kg). I've calculated the Airy points and I'm looking to support it on M8 hex head bolts, with three in contact and two in case of tipping.

My question is: would the M8 heads be ok for size as support points? I've used threaded inserts in the wood with a fender washer and then a locking nut.

Also what if anything should I cover the head with? I have a 3D printer so I was think of some PLA covers but I'm not sure how it would hold up over time with that weight.

Thanks in advance for any help
Steve
 
A broader surface would be better than a bolt head, most plates use some form of hard rubber (like a hockey puck) as the contact surface. For your plate, they would be fine.

PLA covers would have too little strength to be a good choice for supporting the plate.

Wood may not be the best choice for the stand, as moisture and temperature could cause movement, taking the plate out of level. A welded steel frame would be better, if you have access to a welder or materials. 4mm x 50mm angle would work, or thereabouts. Triangulate to prevent weakness under sideward loads.
 
Thanks for the input. I hadn't really thought about the wood being a problem. I don't have access to welding stuff and have never done any welding. I'm getting into machining via a cnc build and I'm interested in getting a lathe but I've done more wood work and 3D printing so all my stands and benches are wood. The main frame is 2 1/4 x 1 1/2 pine with a 3/4 birch ply wood top and osb sheeting to enclose the sides and rear for strength and regidity. I'm not sure how much the engineered woods move?? I'd guess I thought they were quite stable but I guess I'm entering another world in terms of tolerances

If it's on 3 points it should remain planar regardless of movement but I don't really understand when it comes to level. How critical is leveling? I don't have any precision level at the moment just a regular diy level.
 
Lots of cheap metal stands use bolts for the supports. They seem to work fine.

My plate has round metal bosses about 1.5" diameter. It also has two pins that stick up into loose holes in the bottom of the plate to keep the plate from sliding off the stand.
 
Level is not critical, but it's very convenient, as you don't have to worry about round items rolling away on you. It's also good as a reference if things have changed (like wood warping) when you check and find the plate is out of true.

If you're interested in getting into machining then a proper machinists level is handy, and not too expensive if you get one used.

For the stand, use wood now if that's what you must, but keep an eye out for a better version you could buy later.
 
You could skip the bother of a stand for the moment and mount it on a bench top. Its a small plate so the working area around it would come in handy for tools etc. 3 mounts cut from 1/4" mdf would be enough, 2" square/round, dont matter. If your plate has marks on the bottom locate on those if not use the airy points, for an easy life on here ;), shim to level, as milland says so as things dont roll off. Finish off by putting two shims under the free corners so as they just clear the plate, so it can't tip. Sorted :)

Edit: Oppsie, just re read your post, you've already started the stand. Same MO pretty much, stout is good :)
 
I use machine leveling mounts, turned upside down with the "foot" contacting the plate.
These are quite convenient for a surface plate since they're designed to adjust height.

6330kl1l.png


These are effectively single-point mounts, supporting the plate on three specific points rather than over large areas. An advantage is they're also rated to support heavy loads, 500 pounds each or more.

They're quite inexpensive, like $5 each.
Product link: https://www.mcmaster.com/#standard-levelers/=1860d6d
Note that only some of those products are swiveled. Read the descriptions.

- Leigh
 








 
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