Another Joe 2006 - Slightly Modified

[martinw]

Dear mhiggins,

Thank-you for your posts, and I apologise if this distracts you from your fantastic work.

If you have time, perhaps you could help me.

1) How do you ensure that the X axis bed is true and not "racked"? What do you use as a reference "flat plane"? Winding sticks or whatever.

2) Like you, I may be the only one on the glue-up, and the whole process fills me with something approaching total FEAR.

I just do not see how it is possible to assemble all the parts, and maintain accuracy. PVA (water soluble) glue sets up pretty fast in contact with a hydroscopic material like MDF, so maybe an epoxy or phenol formaldehyde glue might be better alternative. That is just a suggestion, and there will be others who have built Joe's machine who can help me.


In the meanwhile, thank-you..

Best wishes

Martin

[Madclicker]

The most important factor in building a flat torsion box is to build it on a flat surface. You will end up with the surface you build it on...or worse.

I don't think segmented cross members in MDF are less strong than a cross lap joint. Try gluing 2 pieces of MDF end to face and then bust them. The failure will be in the MDF of the end glued piece if you glue and clamp it properly. At the very least the segmented construction is plenty strong enough for this application. You need to shoot for flat, not strong. The strength will be there automatically.

Here's a good tutorial on building a good torsion box:

http://www.diynetwork.com/diy/shows_..._26946,00.html

Marks uses segments. Good enough for me.

[mhiggins]

Originally Posted by Madclicker The most important factor in building a flat torsion box is to build it on a flat surface. You will end up with the surface you build it on...or worse. I don't think segmented cross members in MDF are less strong than a cross lap joint. Try gluing 2 pieces of MDF end to face and then bust them. The failure will be in the MDF of the end glued piece if you glue and clamp it properly. At the very least the segmented construction is plenty strong enough for this application. You need to shoot for flat, not strong. The strength will be there automatically. Here's a good tutorial on building a good torsion box: http://www.diynetwork.com/diy/shows_..._26946,00.html Marks uses segments. Good enough for me.

Hey Madclicker where were you about a week ago? This is a truly excellent way of using conventional tools to build the table torsion box. Since that was my original design goal, I think maybe I should go back to it and stop making this more complex than it has to be. I know there are others here who could benefit from this method.
It should be easy for one man to assemble since you glue and assemble in stages. I especially like the sawhorse method that they show for building a flat worksurface. I was going to use my table saw as an assembly table. Two problems with that; one, it's not quite big enough and two, as soon as it is covered in lumber I will surely need to cut something.
I picked up two sheets of 1/2" MDF earlier tonight. I guess if I cut out the skins first I can use those for the work table top while I assemble the framework. If I drip glue on one I can use it as the bottom skin where it won't show. I need to make sure that I have enough 3/4" MDF for the two long sides since I will need that thickness to cut the v-grooves for the pipe rails.
I'll probably be building torsion boxes in my head all night. No sleep for me.

[Madclicker]

My build log started 1.5 years ago. My machine has been running for a year or so.

http://www.cnczone.com/forums/showthread.php?t=14863

My base torsion box is 4 x 4. Wish I had made it a little longer so the cutting area would have been 4 x 4.

You can see from my log that the first thing I did was beef up my assembly table to make it as flat as possible. That table will be my full sheet machine one day.

[mhiggins]

Very cool Madclicker. I see that every part on your machine is a torsion box.

When you glued up your boxes your nailer wasn't working. Did you just rub the pieces together and let the glue hold them as you continued assembly or did you clamp each section and let it dry a bit before moving on or some other method?

[Madclicker]

All you need is clamps for the structure. A pin nailer and glue is best for the skins. I had to make do with all the heavy stuff I could find.

The 4 torsion boxes that make up the gantry make for a very rigid structure. Well worth the effort.

[ger21]

When I made mine, I used polyurethane glue for a longer working time. I shimmed the frame until it was flat by using a 4 ft level and sliding a piece of paper under it. Set the level at al different angles until the paper won't fit under it anywhere. Then glue and staple on the skin. let dry, flip over and repeat. I used plywood for the ribs, it holds staples better.

[martinw]

Originally Posted by Madclicker The most important factor in building a flat torsion box is to build it on a flat surface. You will end up with the surface you build it on...or worse. I don't think segmented cross members in MDF are less strong than a cross lap joint. Try gluing 2 pieces of MDF end to face and then bust them. The failure will be in the MDF of the end glued piece if you glue and clamp it properly. At the very least the segmented construction is plenty strong enough for this application. You need to shoot for flat, not strong. The strength will be there automatically. Here's a good tutorial on building a good torsion box: http://www.diynetwork.com/diy/shows_..._26946,00.html Marks uses segments. Good enough for me.

Dear Madclicker,

Many thanks for that post. I had seen the diynetwork link, and that method gives you all the time in the world for a relaxed glue-up, but I thought that the "segment" method might weaken the panel as regards bending in the direction of the gantry (ie across the short dimension of the bed).

As you rightly point out, all the segments are thoroughly fixed to the "longitudinals" by the top and bottom skins of the box which act as splice plates at each longitudinal to segment joint . As you say, it should be pretty strong. I had not spotted that. Thanks.

One other point... unless you are going to move the whole machine about your workshop, might it not be a good idea, for the sake of simplicity, to leave out the lightening cut outs in the bed? After all, the X axis bed is not being driven by a motor, so there are no dynamic penalties for having extra mass.

It could also be that the X axis bed acts less like the body of an acoustic guitar, and the whole machine is more quiet in operation. Just a thought.

Best wishes

Martin

[Madclicker]

I agree, the bed doesn't need any lightening holes. The only attempt at lightening was on the gantry. I want to try to make much lighter gantry torsion boxes for my next machine. Wish I knew more about composites.

[Marm]

Madclicker thanks for the links to DIY on torsion boxes. I will have to rethink how I was going to make my torsion box now that was great information.

Mark

[mhiggins]

This weekend I got the parts ripped to width for the torsion box build and cut the v-grooves for the pipe rails. I also was able to set up a flat work surface for assembly similar to the one on the DIY website.

I picked up the pipe today and plan to drill and tap it like I did on the gantry torsion box. It's probably not necessary but I like it. I have a three day weekend coming up and hope to make more progress.

[elcam84]

Instead of using a v cutter you can get a 1" diameter bit to make a perfect curve for the pipe to fit in. That's *if* the pipe is actually 1" diameter.


How do you like the 22104 table saw. I have a 22114 for home.