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coherent
04-25-2003, 04:27 PM
I (and I bet others) would be interested in hearing of ideas or experiences for keeping costs down and accuracy/size up. I think most of us are aware of the skate bearings, drawer slides and aluminum window channel possibilities, but what else? Here's a few that worked for me to start the thread off.
-Marc

I'm a ebay watcher and some pretty good deals can be found there if you watch. I'd love to build a $20k cnc router setup, but it's just not in my "hobby" budget (just ask my wife). Here's a couple of low cost alternatives that worked for me:

1. My very first machine used some small diameter steel shafting I scrounged from old printers and oil impregnated bronze bushings which I found at a local bearing supply dealer (about $1 each). If you're not using really small/low torque steppers, they'll do a good job and make for a fairly tight slide unit. You need a good polished shaft for these, or the friction/drag is too high.

2. I got 8 small used NB linear slides and rails for $25 on ebay. The rails were very short (4-6in each or so) and no one was bidding. I priced the rail and it was over 20 cents per mm, or over $5.00 per inch. Enough for one 48" axis would have set me back nearly $500. Ouch... so I bought a piece of uhmw, cut 2 48" strips a little wider than the short steel rail that came with the slides. I ran them through a surface planer making very small adjustments until it was exactly the right width. I then cut a grove down each side with a small ball mill cutter using a router table to match the original rail grove. Now I'm not saying I have the precision that stainless steel rails have, but they are very tight and smooth and I'm using the 2 48" "uhmw" linear rails on my current machine. They work great, and mounted on a flat solid surface support a 36" moving gantry. Total cost was less than $25 for the axis including the small ball mill bit!

3. My lastest find was 13 brand new 1in ID linear bearings (the round kind). You can often get these fairly cheap without the pillow block holders or shafts/supports. I paid $40 for all of them as a "buy it now". I found a metal/steel place and ordered enough 1" turned, ground and polished shafting, (two 4ft, and two 3ft pieces) for a very nice x & y axis for under $60. The shaft is spec'd at +0 to -.0005 which is great for cnc router purposes. Fashion a few shaft mounts and bearing holders out of some scrounged uhmw or aluminum, and you have a pretty accurate and solid x & y setup for a little over $100.

How about you? Any good ideas for Hobby lead screws? Couplers? Slides? Cabling, Cable tracks? Bearing mounts? Details? Pictures? Fess up, inquiring minds want to know!

kong
04-25-2003, 07:03 PM
Gotta love number 2! It's a keeper:D

ToyMaker
05-07-2003, 11:16 PM
Here is my implementation of the Kleinbauer lead screw bearing support. It's just a fender washer with appropriate cutouts for the leadscrew and retainer screws (4-40x1).

http://members.aol.com/ke6njc/myhomepage/xtbrnga.jpg

In the background there is a handwheel I made to drive the axes while I'm building.

robotic regards,

Tom

balsaman
05-07-2003, 11:31 PM
Tom,

Good to see you!

Eric

HomeCNC
05-07-2003, 11:48 PM
Another rail material to look at is Drill Rod. It comes in 36" long and is very accrurate material. Look at the 01 tool steel for .5" dia. catagory, it is $8.51 each.

http://onlinemetals.com/merchant.cfm?pid=4636&step=4&showunits=inches

DLMACHINE
05-08-2003, 12:51 AM
My method is not extreme low cost but it depends on what you wish to do.
I started by buying a used 70's Series 1 cnc Bridgeport for $850, which was in very good shape except electronics. Then bought Larken 3 axis retrofit for $2000.
Now this sounds kinda high compared to you guys, but it's built like a Sherman Tank and will still be here in 100 years. Come to think of it, kinda looks like a tank too. The machine had 3 great high torque steppers and the ways are hand scraped for accuracy. The quick change Erickson 30 taper spindle was a nice bonus as was the variable speed head. The Larken controller gives me a full 3 axis simultanious.
It may not have a big table but it can hog just about anything. With this I can go on to build other machines. Just thought I'd share my machine with you.

ToyMaker
05-10-2003, 10:14 AM
Eric:

Hi. That other sand box got shut down (go figure :confused: ), so here I am.

robotic regards,

Tom

WOODKNACK
05-10-2003, 11:11 AM
Your better off here anyway! We are all glad to give advice out for nothing! That goes for ideas to. Welcome aboard!

kong
05-10-2003, 11:51 AM
I've had some problems coming up with a z-axis design, so ended up using this type (http://www.buildyouridea.com/hardware/cncrouter/phase7/phase7.html). Not my idea, but damn good.
To be honest though, I am finding it difficult to accurately build stuff from MDF, if you have the money, get linear bearings from e-bay.

HuFlungDung
05-10-2003, 12:35 PM
I'm impressed by your efforts, Kong. It still looks like a monumental effort to accurately drill all the holes for mounting your rolling guide bearings, though. How did you accomplish this miracle? :)

kong
05-10-2003, 01:57 PM
Hmmm, sounds like your putting me down....again!:(
Anyways, if you set up a jig on the mitre saw to cut the 45's in the same position, then tilt the drill press to 45, and use a similar jig clamped in place to drill all the holes in the same position, it works.

HuFlungDung
05-10-2003, 02:55 PM
Nope, no put down intended, just a serious question. To make all those wheels contact the rods so it is really "tight but smooth" is a high accuracy operation. Others would be interested to know how you did this, as well as myself.

kong
05-10-2003, 03:09 PM
Ok mate, but I do get the impression!;)
Anyhow, the holes can be cut accurately, but you do need the tilting table on the drill press, otherwise you could make a 45 degree jig from wood. The most difficult part is getting the position for the bearings in the first place! A bit of trial and error here for me, the first part I made had to be scrapped because the bearings were too far back, but the second is good. I have one bearing that is not tight against the rod, but a small shim washer should take up.
Of course I should mention that I made the body and bearings first, then measured for the rods, rather than having the rods in place, then measuring for the bearings - that would have been impossible!

WOODKNACK
05-10-2003, 05:22 PM
I just thought of an idea. Instead of worrying about getting the bearings lined up, Why could'nt you turn down a bolt on a lathe so that the shaft is off center from the thread. ( this bolt holds the bearing down)The bolt would act like a cam. Turn the bolt till the bearings hit just right and tighten the nut down. Hmmm . I love thinking about building stuff..