Gantry design Give it a look

[wcarrothers1]

Well I'm trying to decide how I want to lay out my rails and such on my Y axis gantry layer.. Here are a few drawings..

Baiscly I can't decide if I want to mount the rails to the front surface of my 1"x8" tall plate or if I should mount to the top and bottom.

This plate is also 80" wide.

Still have to decide on what the boxing will be on the back side for extra support..

Since my rails and slides are pretty tall (around 1.88" from back surafce of rail to face of the of the slide I was thinking this would set the front plate off really far away from the plate.)..

But mounting to the face might help with twisting flex of the plate more then mounting on the top and bottom.

Just don't know.

Anyway attached are a few views. Also have to decide how my gantry will interface with the sides for the long axis..

b.

[DonFrambach]

I'm certainly no expert. However, it seems to me that mounting the rails on the front of the plate would allow for very important fine adjusting that would be very difficult if the rails were mounted on the top and bottom.

Don

[lumberjack_jeff]

This is a huge machine. With an 80" wide gantry, I'd suggest boxing it somehow, or use a c-channel instead of plate. It also might allow you to reduce the 200#+ weight.

Once you've guaranteed that the bar won't twist or deflect under cutting loads, mounting the rails top and bottom gives you more mechanical advantage to resist rotation of the spindle around the y axis.

edited to add
Don's point is completely valid. Attaching the rails to the top and bottom requires that the mounting surfaces be parallel to a very high tolerance.

[wcarrothers1]

Point taken on the adjustments. Didn't really thing of that. I think the plate edges should be pretty parallel though..

I do plan on boxing. Actually the 1" plate (8x80") isn't all that heavy. I think it is around 60 lbs as is. Still have to weigh it. basicly I already have a pretty capiable 4x8' cnc machine. this one should be more capiable as the rails and other bits I'm using are more industrial. But everything is going to add up. Hopefully it will work out..

I agree 80" is a little wide. I've only really had a couple cut requests which were > my current machines 50" capasity. Perhaps I should chop it down..

Need the extra to have room for the 2 spindles and to get > 5' capasity. Hopefully things don't get weighed down. Nice thing about this design (I think) if this width does not work so well it can be scaled down pretty easy (shortten the gantry, bring the side supports in and such)..

Will be driving it with large brushless moog servo motors so power to throw the gantry around should not be lacking..

[lumberjack_jeff]

Thanks, I assumed the 1x8 bar was steel. (.29# / cu. in)

If I were to build a (60x120 ?) machine with two spindles, the spindles would be aligned on the x-axis. Building extra-long x causes fewer design headaches than an extra-wide gantry.

I'm partial to the shopbot/mechmate setup; a gantry with two parallel tube steel bars with the spindle(s) suspended on a carriage between.

The rails you show would be a big improvement over the v-groove bearings.

[wcarrothers1]

Interesting idea to align the spindles on the long axis. Not sure how that would work unless the spindles were between 2 gantry lengths (like maybe like a mec mate I think).. But really having them front to back rather then side to side would only save me like 5-7" of width. I have KR slides for the Z which hopefully will make nice ridgid z axis setups with ~8.8" of travel.

The v grove bearing setup on the 1" box (my first router) has been running real well since 2006.. could be better and I'm sure this bar will. I have 6 lengths that are 133" each with 2 trucks (each) so I have enough to re-do my old machine's long axis if I get around to it..

Thanks for the suggestions..

b./

[lumberjack_jeff]

If the spindles are only 6" apart (c-c), 12" additional travel is required to position each spindle within the working envelope compared to the use of a single spindle.

Thus, a 60 x 120 machine with two spindles aligned on the short axis will require 72" of travel to access the whole 60" envelope. Once you add in the overhangs required on each end...

I question whether any single-beam gantry would be stiff enough.

I also think that 6" c-c is ambitious given the diameter of the stepper, the dia of the spindle and the length of the trucks.

Also, I'm assuming that the purpose of the second spindle is for toolchanging, not for making two-at-a-time parts so you don't need two "y" servos.

[wcarrothers1]

My rail trucks are about 6" long. so side to side they take up around 12" as they are. I was expecting to perhaps have some rail over hang the right and left end plates giving me perhaps a little more space.

I understand the point of side by side and having to add length in order to enable both of the spindles can reach the entire envelope.

worst case I've got 80in - 12in = 68" and if my spindles were less then 8" apart I'd have 5ft of reach...

Not sure if 2 spindles would be on both or if 1 would just have my engraving spindle on it. Sorta seems like over kill to have an entire z axis just for an engraver. But I clamp it to my spindle nose and un clamp it once for each engraving job I do. Save me that operation and I"d save some time..

I have been collecting several different G series moog AC motors and L180 moog drives. These are analog which I plan on running with a Kflop and Kanalog setup. Seems to work on the bench quite well. And should pack much more power then my 1100 oz servos and geckos I'm running on my other machine. Also if those are not enough I could go with some Yazkawa step/direction AC servo motors that I got.

b.