Small Fixed Gantry Design

[praneetn7]

Half inch thick steel sideplates in that size are not going to flex much at all, the machine will be a lot more rigid than most people's.

One thing I would suggest is to check all the suppliers for the exact lengths that the linear bearing rails (and ballscrews) come in, and adjust the machine dimensions to suit those so you don't have to try to cut the rails or waste inches with rails that are a tiny bit short etc.

And it also looks as though you could extend the length of the machine a bit without increasing the cost much. This again depends on the standard lengths for rails and ballscrews, but it does look like you could make the machine slightly longer (10%? 25%?) with very little added cost (as the gantry remains the same) so it's worth looking into.

I was going for more of a "desktop" machine so extending the actual frame will not be feasible, however if I do need a larger working area I could use the same gantry and use new 40x80 pieces and rails.

But I did design it with this ebay listing in mind:

linear bearing slide SBR16 (6 supported rails+12blocks) | eBay

As C1 has said I will probably add the triangular side pieces if there is an excessive amount of flex.

As for the lead screws I'm going to be using 12mm, 2 start trapezoidal screws with dumpster AB nuts.

Will 2 start screws make a huge difference over the 1 start for this size of machine?

Thanks

Praneet

[CarveOne]

Will 2 start screws make a huge difference over the 1 start for this size of machine?

Thanks

Praneet

It should theoretically double whatever you get with a one start screw. 4 start will be even better. Any loss of resolution will be less than you will notice when cutting wood and plastics. You can always calibrate the small error out if you intend to cut aluminum to 0.001" accuracies. Do that with the steps per inch (or mm) number.

CarveOne

[Drools]

I'm not sure if Don kept his single start ACME screws on his build of almost the same size. He has a very nice build here http://www.cnczone.com/forums/diy-cn...ry_router.html

[DonFrambach]

I'm not sure if Don kept his single start ACME screws on his build of almost the same size.

I used 1/2" 10 tpi single start screws on my small router until I replaced the x axis and z axis with linear actuators. The lead on one of the actuators is .2" and the other is 5mm. (Not sure if the linear actuators was such a good idea because the acme lead screws and CNCRouterParts linear slides were working fine.)

Hope this helps you.

Don

[praneetn7]

Thanks Don,

Did u find that the ballscrews in the acuators make a huge difference in accuracy over the acme?

I probably will stick to the 2 start Trapezoidal as it is only going to be about $20 extra and will theoretically double my speed.

TBH I did get my inspiration from your machine.

Thanks

Praneet

[DonFrambach]

Did u find that the ballscrews in the acuators make a huge difference in accuracy over the acme?

I can detect no difference in accuracy or quality of cut between my old system with acme leadscews and the linear actuators with ground ballscrews. I'm making fairly detailed wooden carvings using mostly 1/8" ball nosed bits (sometimes 1/16"). There is very little cutting force when making these fine cuts. When I set up my acme leadscrew system, I could detect no backlash with a cheap Grizzley indicator and no cutting load.

I typically cut at 20-30 ipm with my acme leadscrews. I'm hoping that I'll be able to cut substantially faster with the ballscrews. I hope to reduce 20 hour jobs down to 5 hours. (That's the only way I can "justify" the expense and hassle of the actuators.)

[praneetn7]

Most of the things that i will cut will be shorter runs (like 1-2hr jobs or less).

Well from what I have heard the trapezoidal will do just fine

I am going to have the thrust bearings between the radial bearing and a collar to secure the screw and on the stepper side i will have a thrust bearing between the radial bearing and the shaft coupler will secure it down.

Does this make sense? I couldn't rephrase it any other way..

Praneet

[DonFrambach]

Most of the things that i will cut will be shorter runs (like 1-2hr jobs or less).

Well from what I have heard the trapezoidal will do just fine

I am going to have the thrust bearings between the radial bearing and a collar to secure the screw and on the stepper side i will have a thrust bearing between the radial bearing and the shaft coupler will secure it down.

Does this make sense? I couldn't rephrase it any other way..

Praneet

I think you will be pleased with your choice of lead screws.

I think I understand what you're saying about the thrust bearings. To be clear, you need to have two thrust bearings, one on each side of something fixed to your frame. You don't want to use the bearings in the motors as thrust bearings. Not recommending that you do what I did but I just uploaded a photo of the bearings I'm using. Here's a link: New DYI Fixed Gantry Router Build (The photo on the left shows some tapered roller bearings I'm going to install. The second photo shows much simplier and much less expensive thrust bearings that I purchased from CNCRouterParts.)

[praneetn7]

So would this be suitable?

Yellow = Thrust bearings
Red = Bearing blocks with radial bearings
Green = Lead screw

Praneet

[DonFrambach]

So would this be suitable?

Yes

[draughted]

for ballscrew end bearings you should be looking for cheap chinese
ballscrew endbearings in the FF and FK type, and have your ballscrew or leadscrew machined to suit.
I like your side panel members, they are similar to mine. You should think about doing the same thing on the Y axis ends, but do them in aluminium, maybe about the 16 to 20mm that the others were saying.
it is the ballscrew end bearings that got me too.

[draughted]

i also got my bearings from linearmotionbearings2008.
don't define your machine around the parts you find of their site, ask for an email address and go through a quoting proccess to get exactly what you want.

his ballscrews are nice and cheap, don't rule them out just yet, he will get them machined at a really small fee.
however last time i asked he would not supply those FF and FK end bearings you'll have to find another supplier.