New User - New Machine

[mmonti]

Hello everyone. After lurking around the forums off and on for what seems like years and always wanting to build one, Im am now in the process of building my first CNC Router.

Dimensions are a 36x24 steel base. The goal is all aluminum construction with the steel base. I have a table that it will be sitting on. I plan on using vxb 20mm linear rods and bearings. Thinking about using the fully supported 20mm vxb rods and open bearings for Y axis, was going to use the excess cut off from my X axis for the Z axis, 15 inches long?

Im basically building this as I go. I know the general direction I want to go for the finished product. Looking for some design assistance and help to prevent big errors.

I had a metal shop build a frame for me, I just finished priming the frame ( ran out of primer) and set the linear rods and bearings on to get a look.

I plan on supporting the X rods about every 10 inches, Ill be cutting that aluminum T to fit. I would've liked the fully supported rods but they are just a lil pricey, im not looking for absolute accuracy as I wont be building my space shuttle until I can build a bigger & better machine.

Im attaching a few pics of my progress so far, this has been a slow build compared to some of the others I've seen being built here.

I do have my first question...
I want to make sure my X rods are aligned properly before I drill and tap the base for the rod supports. Whats the best way to do this? Should I build out a template of the gantry bottom with some cheap(er) material and clamp and adjust until the rods are parallel?

Thanks everyone for the inspiration to finally build this.

Mike

[ahren]

Hey Mike,
Welcome to cnczone! Looks like a solid frame, and I like how you have things set up for a center drive that runs under the table.
As for your rod supports, I think you're on the right track with clamping and checking. I think you might go ahead and build your gantry before drilling any holes. That way, you can move the gantry to one end, drill and tap for the rod supports, and then run the gantry down to the other end to help locate the rod supports on that end.

Ahren
www.cncrouterparts.com

[johnmac]

Mike, your off to a good start. If you have enough T aluminum for more supports, add them. you won't regret it. Don't build it "just good enough". Strive for the best that you can. Enough imperfections will creep into the build anyway. Its hard to go back and fix slop.

I won't say how I know that. But I will say I'm on build number two!

John

[mmonti]

That's a good idea Ahren, I'll build my gantry before I drill any mounting holes to insure everything is aligned perfectly. You are correct I was planning on a center drive acme screw. I was going to use 1/2" acme I'm thinking it will be fine for this application.

I have 2, 3/8 aluminum plates 6x32 inches or so, that I will be cutting to fit for the end pieces, I'll drill those out and mount bearing blocks on those for the X screw.

Johnmac, I can get more of the T extrusion, what would be adequate? 2 inch pieces every 5 to 8 inches or so? The total length is 40" I know the 20mm rod looks substantial but there is a bunch of flex in em at a 40 inch span, and Im not sure what my gantry will end up weighing. I'm estimating aprox. 40+ lbs based on my drawings and 6061 weights.

I have an initial template cutout of cardboard for my gantry sides at 21.5 inches tall, by 8 inches at the base where it mounts to the bearings. I'm not sure if that would be good on here. Looks tall mocked up and seems like the gantry will eat alot of my cut area up. I have planned my Z to be 13.5 inches tall by 5.5 wide. I need to finish the drawing in rhino before I finalize it.

Thanks!

Mike

[johnmac]

Mike, 2" pieces every 6-8" sounds good to me. Don't be surprised if the gantry ends up weighing quite a bit more than that. Keeping the overall height as short as possible will add strength as it will not try to flex as much. That goes for the Z axis, as well.

If your going to acme screws, use 2 start or 5 start screws. If you use single start screws, the maximum travel speed will be rather slow.

John

[mmonti]

Can anyone here make this part? I need 2 of these for my Z axis top and bottom. Its a 1/2" x 2.5" x 5.5" block of 6061 with some 20mm holes for the linear shafts. I tried to get it as accurate as I could, but starting with inches and then working with metric for the bearings has been a pain in the @##, all the measurements ended up in metric. the center hole will be drilled to hold my bearings for my lead screw. any suggestions on size for that?

Mike

[mmonti]

Does anybody know which are the correct bearings to use for 1/2 acme rod? Ive been looking on the dumpstercnc website where I planned on buying the anti-backlash nuts and he has a couple mcmaster-carr part numbers listed for acme screws. There are no bearings listed.

Which is the best route to take as well? 2 start or 5 start, the price doesnt seem to be great between the 2. Also if I purchase a 6ft rod, can I just hacksaw it to size for my XYZ axis? Seems the lengths go from 36" then jump to 6'

Thanks for the help.

Mike

[ahren]

You need 1/2" bearings for the screws, unless you are planning on turning the screws down to fit another size. I offer bearing blocks that work with 1/2" ACME on my site. Alternatively, you can make your own holders, and vxb sells 1/2" bearings.

Ahren
www.cncrouterparts.com

[CarveOne]

Originally Posted by mmonti Does anybody know which are the correct bearings to use for 1/2 acme rod? Ive been looking on the dumpstercnc website where I planned on buying the anti-backlash nuts and he has a couple mcmaster-carr part numbers listed for acme screws. There are no bearings listed. Which is the best route to take as well? 2 start or 5 start, the price doesnt seem to be great between the 2. Also if I purchase a 6ft rod, can I just hacksaw it to size for my XYZ axis? Seems the lengths go from 36" then jump to 6' Thanks for the help. Mike

Many people use 1/2" inside diameter by 7/8" or 1-1/8" outside diameter by 5/16" thick skate bearings. http://www.vxb.com and other places have them.

5 start will give faster jog speeds at a given rpm than 2 start if you have the proper torque stepper motors to drive them. 270 oz/in to 425 oz/in can usually work with either 2 or 5 start lead screws. Depends on the gantry weight and drag to some degree also.

You can easily cut ACME rods with a common hack saw. Just file the ends square or do it with a disk sander if you have it.

CarveOne

[mmonti]

Thanks for the information. I wasnt going to select steppers until I was closer to that stage, figured if it ended up being heavier than I expected, I would want to get the right motors.

Ive almost finished my gantry drawing, gonna try and post it this evening if I get the time. I will be picking up some alum. next week for the remainder of the gantry and talking to some people to cut everything to size.

Anyone ever drilled aluminum with a forstner bit? Might give it a shot, I only need 6 holes for my bearings, alum is fairly soft

Mike

[johnmac]

I used a hole saw to drill large holes in 1/4" aluminum when making my motor mounts. I used a better quality saw in my drill press. I clamped the aluminum to a piece of lumber, kept the cut wet with WD-40 and about half way thru I turned the aluminum over. Once the hole saw teeth get below the surface, the chips can't exit and cutting slows real fast.

John

[mmonti]

Heres my Z axis drawing, its missing a few things, bolt holes, Y bearings, and the bearings for the lead screw, but this is the basic idea of it. Id like to keep it as simple as possible but as strong and light as possible, I cant remember the diameter of the router mount but I wanna say it was measured for a porter cable.

I'm having a difficult time determining if my X gantry side pieces width should be 8" or 6" in width, or maybe even slimmer? Also what is a good height? I was shooting for about 20-22 inches high. I planning on using 3/8 or 1/2 aluminum stock for this. Any suggestions.

Mike