design idea.

[oneturboneeded]

what do you guys think of a liner rail on both rails on x and one on y. and having a spring loaded rack and pinion to drive them on the side of the square tube making the table.

[Robin Hewitt]

I'm designing a table at the moment

Are you suggesting driving one end of the gantry arm and hoping linear bearings will keep it true?

I'm using puny 160 oz.in disc magnet motors, but after allowing for losses there will still be around 80 lbf accelerating the gantry.

With a rack at either end and two pinions on a cross axle you only have to counteract twist. Remember that the pinion will try to rise out of the rack when you start applying that big acceleration, so are you sure about those springs?

On the down side, getting a pulley in behind the pinion at one end without weakening it...

[massajamesb]

actually, both sides of my X have bearing slides (of my own making/design), and I have one motor driving both sides via a jackshaft, and both pinions are spring loaded via 300lb return springs. Works well, I think. Keeps backlash to a minimum.

[oneturboneeded]

yea i was thinking of just driving one side but will the twist cause the bearing to load and stop?? what about putting two bearings on both sides to spread the load.

[massajamesb]

With a homebuilt bearing assembly, you might see some "racking" at higher speeds. With the more expensive linear bearing slides, you will probably be in good shape. If your gantry is weak and/or thin walled, you will see a lot of flex problems from that, too.

If your bearing trucks are of a decent length, so the force is spread out over a certain distance, you should be able to keep out a lot of the flex, versus trucks that are not very long.

My bearing trucks should really be longer than they are ( 8 inches between the bearing centers) because until I used the jackshaft method, I got quite a bit of racking, even though both sides of X had bearing slides, and bearings gripped all 4 sides of each CRS slide.

[oneturboneeded]

What would be better a linear bearing rail with the trucks 10 inches a part on one side. on the other side a simple roller bearing truck or a linear bearing would it make a big difference?

[Robin Hewitt]

Originally Posted by oneturboneeded What would be better a linear bearing rail with the trucks 10 inches a part on one side. on the other side a simple roller bearing truck or a linear bearing would it make a big difference?

It isn't so much the separation of the trucks, it's flex in the y axis rail and you will put an s bend in the x axis rail. Not a lot, but it will be amplified when the torch carriage moves out.

It could be fine, depends on the overall dimensions, acceleration, precision you are trying to achieve and sheer weight of metal you are prepared to use keeping that x axis rail straight.

It is possible. There was a recent thread on a chinese cutter that had absolutely no support at the far end of the gantry. It gave great access for loading plate but the x axis rail was enormous

[oneturboneeded]

should i just drive both sides then? how much harder is that? i need a gear box or double belt drive or 2 motors can that be done??

[oneturboneeded]

o and i own a offroad fabrication shop. for now i have a hypotherm powermax 350 but i will eventually go with a 1000. i want about 12 to 14 inches of up and down so i can use a router also for doing molds for carbon fiber stuff. for now the thickest i will cut is 1/4 plate mostely 3/16. i want a nice round hole for bolts to fit through the tabs i cut. sorry i kinda jumped around there.

[Robin Hewitt]

Originally Posted by oneturboneeded should i just drive both sides then? how much harder is that? i need a gear box or double belt drive or 2 motors can that be done??

You make up a long shaft with a pinion and rack at either end. If your y axis is box section, you can put it inside

[massajamesb]

2 motors can be used, but I only have one, and it drives a belt reduction on one side of the table, and that drives a shaft that has the spur gears on both sides of the table.
If this doesn't make sense I will try and get some good pictures of the arrangement up.
Clean circles are possible with plasma, but I suggest cutting your holes about 1/16 smaller than you need, then finish drilling them to the exact size needed. Especially with the 350 series Hypertherm in 1/4 plate.

[oneturboneeded]

yes some pictures would be sweet. is a 350 hypotherm crappy?? or just to small.