BrainStorming Help !!

[angus_hines]

OK so I have the 12" Z and not always needing the 12".

I was contemplating a table with automated adjustable height, like the table in my laser that goes up and down with the push of a button.

With that in mind.
Should I make some sort of Ball screw lift or maybe a hydralic lift? Rak and Pinion type lift?

And how would I connect it to be controled through the outputs in the SB control box?

Gary C. ??? I know you have the answer....LOL Help trick my Bot !

[bleeth]

Angus: I would probably use a ball screw. One motor and chain. Dozens of power plane makers can't all be wrong!!

[Gary Campbell]

Angus...
First, descide what will hold you back, your imagination or checkbook!

Dave is right, ball screws and chain are the way to go. 6 or 8 with an alpha stepper controlling them for adjustable height.

Remove table boards, reinforce cross braces and make assemblies to hold ball screws and motor.

2" aluminum square tube movable table frame with lightweight fiberglass composite for bottom. If you pay attention to your design, it will be vac plenum also with Trupan top over aluminum defined zones.

Next time be careful who you ask!

Gary

[rb99]

How about using the lifts that are used for adjustable counter height for handicapped people?

RB

[Brady Watson]

You'd save yourself a lot of agg if you just build a 5 or 6" torsion box & attach it to the table.

-B

[angus_hines]

Thats what I keep coming back to Brady. I can't seem to figure a way t o prevent all the flex I would have if I did a Adjustable table.

This isn't a real need just an idea I've been playing with in my head. The new Z axis holds really well @ 10" of Z cutting 400 ipm. No chatter or anything.

And Gary I ask you because when it comes to trick'in out a Bot you got the answers.

Pat "Frank" on the head for me this AM

[kubotaman]

Brady, Can you please explain what a "torsion" box is. I am interested in a table so my 12" x-axis may be a little more accurate. I have addressed this issue a few posts ago. Thanks!

[dray]

I would go with torsion box as well. $100 in material and just set it aside when not using it.

[carlosgmarroquin]

DIY_14350_26946%2C00.html,http://www.diynetwork.com/diy/shows_wwk/episode/0,,DIY_14350_26946,00.html (http://www.diynetwork.com/diy/shows_wwk/episode/0%2C)

Don't know if I copied the link correctly, but you can paste on the browser begining from the http:// ...

Hope it helps

[oddcoach]

A torsion box has a grid of strips at right angles to each other and then glue a sheet of plywood to each side
I would use 3/4 plywood for the strips. Just rip them to the thickness of your box minus the skin thickness the skins do not need to be very thick
you could use 1/4 inch on the bottom. the strips do not need to be half laped at the intersections.
just make one direction full length and cut the others to fit in between
Hope this helps

[oddcoach]

A torsion box has a grid of strips at right angles to each other and then glue a sheet of plywood to each side
I would use 3/4 plywood for the strips. Just rip them to the thickness of your box minus the skin thickness the skins do not need to be very thick
you could use 1/4 inch on the bottom. the strips do not need to be half laped at the intersections.
just make one direction full length and cut the others to fit in between
Hope this helps
6594

[henrik_o]

Torsion boxes are super. One problem is that once you're dedicated to a format, it is usually not that easy to change -- nor to change out. Fastening a t-box from beneath is a clinch, but what about fastening the actual table structure to the torsion box?

As a fellow twelve inch member, with the bragging rights this inherently grants (har har har), some kind of semi-open torsion box is probably a great idea, but you don't actually need it.

Following is a couple of pics of our setup snapped during a change of the substrate support (to change table height, this is why not all bolts are in place).

This is for practical purposes --in my experience -- as stable as a torsion box and considerably easier to build. You can make several sets of differing heights, and it all stashes away without demanding nearly the same space proper t-boxes would crave. It takes about an hour to swap out for a different set.


6595

and


6596


One more thing, snapping away at 400IPM in board material with a 10" z does work with little chatter, but just wait until you're starting to cross toolpaths or work with less homogenous material. You will se considerable flex, there just is no way around it. The good thing is that us 12 inchers _have_ to build an extended table substructure and as we do so we can just as well build several as long as they're relatively easy to build and to swap out and in.

I have one set of supports which provides just half an inch of clearance when cutting 1/2" ply.

The speeds we can achieve with that if a job calls for it is very close to pushing the limits of the machine as by Shopbot specs.

Just saying.

[carlosgmarroquin]

Thanks for the info Henrik. It will help a lot. I have been fighting a little chatter myself.

[henrik_o]

Carlos,

For the 12" people, it is a necessity, but for those that run production 'bots I think it is a very good idea none the less. The difference beteween having a 5" and a 1/2" clearance is *vast* in terms of practical machining speeds for close tolerances. You learn to live with having to do tool changes off table (don't build it too large as I nearly did!) at least as long as swapping can be done with relatively little effort.

Our standard substructure set provides about 5" free z travel from table top to collet bottom. That means 19mm MDF *one-passed* at about ~100IPM when doing close tolerances. With the 2" clearance set, we can do ~250IPM.

If you are cutting the same thickness material day in and day out, it really makes sense to tailor your table to that.

Your mileage might vary but it's been my experience.

For those of us with Alphas and the bosch style gantry, there's probably few modifications that can give as much increased speed / precision as tailoring the table height.

[henrik_o]

Also, on a practical note: the top and the bottom of the double-tee support is of equal lateral dimension in the pictures above (i.e. the sections which contact the steel frame and the bottom of the actual table are of equal horizontal size, respectively).

This makes it needlessly difficult to swap it out and greatly contributes to the time it takes to do that: the bottom can be rapidly unseated with a makita impact driver because there's no space constraint but the top requires manual unseating since there's not enough space to do this with a power tool.

The reason why it was done so? Because we started with a full z table, and drilled the holes in the actual table in those places, corresponding to the pre-drilled holes in the steel frame.

In order to change the hole placement, we would have needed to redo the whole table. We have a good table -- we didn't bother.

If I was to redo this, I would absolutely space the bolts fastening the table to the substructure double-tees further apart, such that a handheld power tool can reach the tops in the direct drive position (no adapters and no leaning the tool).

It takes us one hour to swap sets now, down from about two hours when we first did it. With the above changes, it should be doable in half an hour.

If the above is fuddled or unclear I'll do my best to straighten it out, post here, email or friend me on facebook: ' Henrik Olofgörs ' (or if you can't use the umlauts just use 'Henrik Olofgors' and choose the one profile it suggests.

This goes for everyone, we should get better at facebooking each other.

[bcammack]

I'm thinking "T-nuts" on the inward facing sides of the top/bottom plates. Unless the heads of the upper bolts are buried in the underlying layer of the top.

In that case I'd bury the T-nuts in the underlying layer of the table and bolt upward into them.

[carlosgmarroquin]

Henrik. Thank you for the information, I'm finishing a project right now and then I will give it a try.