How to remove flex from table

[hualon]

My machine has a 24x12 cutting area. The top (bed?) that came with it is 3/4" plywood but it is warped and so the middle is considerably lower than the edges.

The top/bed spans the entire 24 inches without any support except for at the two distant edges (which are 3/4" HDPE).



So I was thinking about replacing the bed with a more rigid material that wouldn't bow and that would be dead flat across the entire surface. What kind of material do you think that I should use?

I was thinking about 1" thick UHMW but I worry that that might bow in the middle under its own weight! I've seen some beds that use some square metal tubing that has channels cut in all sides which seems like a good idea but I'm not sure what it's called.

Any ideas?

[High Seas]

hualon -

The UMHW would probably bend as you suspect - just like the ply - if unsupported.
Add a few "floor joists" --just like in your house-- and you'll keep the sag and warp out of either. Plywood would be way cheaper. It looks like you'll have to work around the mechanism under the table - but I bet its do-able.

Jim

[CarveOne]

hualon,

If that were my machine I would replace the bed with a flat aluminum plate and then use something else on top of it for waste material. Use your machine to skim the waste material top surface true over the available cutting area. That size aluminum plate should not be so terribly expensive though it will cost some money.

Also, if the table top it is sitting on is not perfectly flat the machine's bed may be assuming the same twist or warp to some minor extent. There doesn't appear to be enough structure in the base to resist diagonal twisting. I can only see a flat plate at the bottom and the two upright end pieces forming a "U" shaped structure. The top plate ties the "U" across the top, but there is no good way to close the box on the sides and make it more rigid than the table that it is sitting on. If the gantry doesn't extend across the machine under the bed maybe some vertical plates can be added to tie the top plate to the bottom plate to turn it into a torsion box.

I don't mean to be criticizing, just pointing out some possibilities to look at.

CarveOne

[hualon]

Originally Posted by CarveOne turn it into a torsion box. I don't mean to be criticizing, just pointing out some possibilities to look at.

I really appreciate the input. I don't see it as criticism at all. I'm pretty frustrated with this machine and I wouldn't buy it again if I had it to do over again.

I was thinking along the same lines as you were with the aluminum/sacrificial top. Do you think that .5" Al is sufficient or should I go thicker?

[High Seas]

Oh - BTW the aluminum channel you were asking about is 80/20 -- there is a surplus site here on the 'zone - and they are at eBay too. Bolts together well - and a plus is you can use it for part hold-down too. Probably could use the smaller sizes -- and they have a flex calculator if you google them and go to the website.

Jim

[CarveOne]

Probably 1/2" to 5/8" plate will be stiff enough for this size machine. If the plywood plate is 3/4" then use 3/4" aluminum plate if you can afford it. That would keep the dimensions of the z travel as it is now, and would allow you to have maybe three T-slots machined into it if you should want them. Otherwise, you can drill a pattern of holes and thread them for hold downs without substantially weakening the plate.

Take a look at the inside of the base and see if there is any reasonable way to glue and screw in some vertical interlocking pieces of plywood or MDF to turn the base into a torsion box if it is not that way already. The x axis lead screw will require a hole in each piece. If the gantry ends are connected together under the top plate you can rule out the torsion box idea as there is no room for it..

CarveOne

[wyldesyde007]

here's an idea for you that might be a quick fix.