accurate is subjective
Balsaman,
What do you call accurate?
I plan on cutting 3/4" oak plywood in one pass and hope to achieve <= 1/64"
If you build the machine nice and tight you will be fine. The problem comes in when you are cutting close to the side of the gantry. The screw is in the middle, so the gantry wants to skew. I would consider making the gantry sides wider, so that there is more space between the guides. The moving table scheme eliminates this problem because the guides are spread way out at the corners of the table.
Eric
I wish it wouldn't crash.
Sol,
Thanks for the link. I really like the wooden bearing mount part. I think it can be made easily with aluminum. Any foreseable shortcomings?
Last edited by abasir; 01-08-2004 at 04:24 AM.
Stupid questions make me smarter...
See how smart I've become at www.9w2bsr.com ;-P
Sol,
This is a super "out of the box" design. I especially like the alternative tension adjustment.
Hager
Last edited by Mr.Chips; 01-08-2004 at 08:30 AM.
sol
I like the idea of "dumpster diving" in your own shop. Nice proof of concept too. Just wondering what sort of "accuracy" you get? Precission and repeatability would be a nice reference to lay alongside overall cost. Could you provide here, in a PM or on your site?
I say congradulations - your results should certainly make others getting started less intimidated.
Jim
Sol,
How about posting your machine on a new Thread? All new machines deserve it.
It helps future builders go back and look at the design for ideas.
Hager
How does one measure precision and repeatability?
Do I just use calipers and measure something?
Mike...
I've seen a number of pictures where the stepper motor has a belt drive to the ball screw/thd rod.
What's the benefit or disadvanted of using a belt drive. I was going to have a direct drive on mine, with a fixed coupling between the axle shaft and the threaded rod.
Can someone tell me which way is better?
TIA
Mike...
For a DIY "cheap machine" I think direct drive is the way to go with stepper motor. Its a good example of the KISS principle.
I feel that the timing belt gear reduction is better suited for servo drives where you want to keep the speed of the servo up and gear down the turning of the lead screw.
Answering your other question about measuring precision and repeatability, I make a test program and have the router make a test part, say a 10" square or 10" circle. I then measure the piece and record my measurements. If you make 100 parts and they are all 11" exactly, then you can say that your machine is very repeatable, but not very accurate.
How accurate you want it to be depends upon your needs. +-.004 per foot sounds good, but that is +- .032 over 8 feet. Is that good enough? Only you can decide.
Another way to check is to put a dowel in the collet and jog the machine to a known coordinate. Then measure the distance against a solid surface, The machine itself, a wall, etc. Jog the machine again and measure again. You can use calipers, tape measure, dial indicators, or a string with knots in it. Again it all depends upon you needs.
Personally, I use digital calipers dim's under 6". a dial indicator for checking flatness of the table, and a tape measure for long dimensions.
>get the 116 oz steppers from Xylotex
Hey Balsaman,
Why wouldn't I get the bigger nema 23 stepper, i.e. the 253 oz? Isn't more torque usually better? Especially if I want to hog out more material at one pass...
Mike...
http://www.pacsci.com/products/step_...xproducts.html
lead screw retension
Can someone illustrate to me typically how the lead screw(s) are retained?
I assume that this allows the screw to rotate within the bearing which is fixed but not allow the screw to move laterally in either direction by "sandwiching" it between washers/nuts and having a retaining plate hold the whole thing in place?
Also assume that the other end has another bearing to support that end as well, then connected to the step motor using a coupling?
Well I can certainly illustrate what I see!!!
In the picture below, you see the coupling that connects the motor shaft to the threaded rod.
The lower shot is where the threaded rod goes thru the anti-backlash nut.
The other end just hangs there in space... in a 2 1/4" clearance hole actually. I might be inclined to capture that in some fashion to keep it from whipping around...
Mike...
Last edited by mikeschn; 01-08-2004 at 06:33 PM.
I wasn't going to include a picture of the hole... but what the heck...
Here it is...
Mike...
Because they cost at least 4 times as much, unless you can find used ones. And for what Jeff at Xylotex charges for them, you won't be losing much if you upgrade later. On that note, On the Xylotex group Jeff said he probably won't be selling them for much longer, so get them while you can. As for the 253 oz, I got 4 last april on Ebay for about $60 each, but haven't really seen any since.If you can find them for a good price, or don't mind paying, get the bigger ones.Originally posted by mikeschn
>get the 116 oz steppers from Xylotex
Hey Balsaman,
Why wouldn't I get the bigger nema 23 stepper, i.e. the 253 oz? Isn't more torque usually better?
Gerry
>How accurate you want it to be depends upon your needs. +-.004 per foot sounds good, but that is +- .032 over 8 feet. Is that good enough? Only you can decide.
Hey buscht,
Really? out by that much? So when you hear someone talking about a +- .0025 tolerance, they are really talking about the stepper motors, not the completed system, right?
The completed system would have to be parallel and perpendicular so that you are not out by .032 over 8'.
Mike...
Oh Balsaman,
Jeff no longer sells the motors. He recommended some guy on ebay... see this auction... 2586416419
It's currently at $81. How much do the 116oz motors go for normally?
TIA,
Mike...
I think he was selling them for $20.00? You can always wait. Lot's of steppers on ebay. You want 5 or 6 volt ones.
200+ oz is is nice and quite manly, but expensive and hard to drive. xylotex only drives 2.5 amps MAX. You need Geckos after that. $375.00 for 3. On a wooden machine you should not be "hogging" anything. 100 oz in steppers will do more than you think. I was using them and could cut up to 3/8" deep in one pass at 20" per minute.
.032" is 1/16 of an inch, over 8 feet, that will do for most hobby people. We usually make trinkets after all.
Eric
I wish it wouldn't crash.
Mike,
thanks for the pics! just what is an anti-backlash nut?
With the stepper motor turning to push/pull the gantry I would think that it would be better not to put these stresses onto the stepper motors. I would think that a better design is to support both ends of the screw...
Actually, .032 is 1/32", but you already new thatThose motors on Ebay are the same one's Jeff was selling. He was buying them from the same guy. He must have a million of them, because he always has some for sale. Depending on the time of the year, they go for anywhere between $60 and $120 (for 4). If you want new ones, here's a place you can order from online (with prices).
http://new.kimcontrols.com/category/...fic-Scientific
Gerry
Hey dlenox,
Here's a good illustration of an anti-backlash nut...
read all about it here...
http://www.wmberg.com/article970324.html
Mike...
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