Build Thread- 8020/MDF Hybrid Desktop

[jwillhite]

My interest in cnc has remained after playing around with a hacked together desktop plotter/cnc for the last couple of months(see it here: http://www.cnc.draft-design.com)

Now its time to build a real machine. I've taken inspiration from a lot of builds here on the zone, thank you guys. In particular Snowgrains I think turned out really well http://www.cnczone.com/forums/showthread.php?t=53316.

My budget for this project is 1400-1600, I'm not sure if thats possible but thats what I'm shooting for. Due to the cost of the 8020 and the fact that I have access to mostly hand tools I plan on going with an aluminum extrusion and mdf hybrid. I can order the extrusion to length then tap it myself, I don't think I want to try and cut it though. Looking at what Ahren has to offer at http://www.cncrouterparts.com/index.html, that should pretty much take care of the linear bearing assemblies.

Here's what I'm thinking so far:

The bed is 24"x36", the actual cutting area will be more like 24"x26". If anyone sees any potential flaws or anything that could be improved I'd really appreciate the feed back.

Also I'm trying to decide on the stepper motors, should I go with 282oz.in motors or would something larger be more appropriate? Does anyone have a link to a build log that shows the electronics being put together from scratch? I'm debating whether or not to try that. The electronic controls for that little plotter I built went together without a hitch, not sure how that stuff would scale though.

-Josh

[TOTALLYRC]

Originally Posted by jwillhite My interest in cnc has remained after playing around with a hacked together desktop plotter/cnc for the last couple of months(see it here: http://www.cnc.draft-design.com) Now its time to build a real machine. I've taken inspiration from a lot of builds here on the zone, thank you guys. In particular Snowgrains I think turned out really well http://www.cnczone.com/forums/showthread.php?t=53316. My budget for this project is 1400-1600, I'm not sure if thats possible but thats what I'm shooting for. Due to the cost of the 8020 and the fact that I have access to mostly hand tools I plan on going with an aluminum extrusion and mdf hybrid. I can order the extrusion to length then tap it myself, I don't think I want to try and cut it though. Looking at what Ahren has to offer at http://www.cncrouterparts.com/index.html, that should pretty much take care of the linear bearing assemblies. Here's what I'm thinking so far: The bed is 24"x36", the actual cutting area will be more like 24"x26". If anyone sees any potential flaws or anything that could be improved I'd really appreciate the feed back. Also I'm trying to decide on the stepper motors, should I go with 282oz.in motors or would something larger be more appropriate? Does anyone have a link to a build log that shows the electronics being put together from scratch? I'm debating whether or not to try that. The electronic controls for that little plotter I built went together without a hitch, not sure how that stuff would scale though. -Josh

Nice drawing and design.

282's should be more than enough.
Trying to run a nema 23 size motor on home made circuits is a false economy in my opinion. Going low cost on the electronics means just that, you have low cost electronics. If you go better on the drives and such, you can always move them to another machine or back and forth, when you have 2 machines. With low cost mechanicals, you can always use the machine to make parts for a better one or do parts upgrades one at a time.

Having used a Xylotex board on my Taig for a while and now seeing what the G540/250/251's can do. $299 gets you a heck of a lot of capability.

Xylotex 4 axis $185. 35v and 2.5amp absolute max 87.5 watts max/ motor.
Breakout board $75 for a decent one.
VFD control board $30 and up
Total $290
G540 All of the above bulit into 1 and the 4 drives are modular. if one goes bad it is 5 minutes to swap out.
$299 http://www.geckodrive.com/product.aspx?c=3&i=14469
50V and 3.5 amps conservative ratings. 175 watt / motor
The actual way that it drives the motors is 100 times better than any other low price drive on the market.
Double the power for a few dollars more. IT IS A NO BRAINER

Many peope will say I can go slow, after all it is just a hobby. The laws governing how well a cutter cuts don't care what your budget or wife says, there is a certain minimum speed you have to go or it burns the work or dulls the cutter or gives a lousy finish on the part.

I have 2 machines ( router and mill) that, If I knew then, what I know now, I would have done the electronics differently. The newer gecko drives I mentioned weren't even available at the time.

[jwillhite]

Originally Posted by TOTALLYRC Nice drawing and design. 282's should be more than enough. Trying to run a nema 23 size motor on home made circuits is a false economy in my opinion. Going low cost on the electronics means just that, you have low cost electronics. If you go better on the drives and such, you can always move them to another machine or back and forth, when you have 2 machines. With low cost mechanicals, you can always use the machine to make parts for a better one or do parts upgrades one at a time. Having used a Xylotex board on my Taig for a while and now seeing what the G540/250/251's can do. $299 gets you a heck of a lot of capability. Xylotex 4 axis $185. 35v and 2.5amp absolute max 87.5 watts max/ motor. Breakout board $75 for a decent one. VFD control board $30 and up Total $290 G540 All of the above bulit into 1 and the 4 drives are modular. if one goes bad it is 5 minutes to swap out. $299 http://www.geckodrive.com/product.aspx?c=3&i=14469 50V and 3.5 amps conservative ratings. 175 watt / motor The actual way that it drives the motors is 100 times better than any other low price drive on the market. Double the power for a few dollars more. IT IS A NO BRAINER Many peope will say I can go slow, after all it is just a hobby. The laws governing how well a cutter cuts don't care what your budget or wife says, there is a certain minimum speed you have to go or it burns the work or dulls the cutter or gives a lousy finish on the part. I have 2 machines ( router and mill) that, If I knew then, what I know now, I would have done the electronics differently. The newer gecko drives I mentioned weren't even available at the time.

Thanks for the advise/info, its invaluable at this stage when I'm buying the pieces.

Pretty sure I'm going to go with the G540, originally I was thinking about buying a kit like this from Keling Inc. http://cgi.ebay.com/3-Axis-Stepper-M...742.m153.l1262
The G540 including power supply and steppers is going to run about 500.00 not including shipping vs. the Keling kit which is 440.00. I think your right about not skimping on the electronics though, that and the G540 is such a clean simple plugin solution.

Looks like the Keling power supply I was going to buy(http://www.kelinginc.net/SwitchingPowerSupply.html) is out of stock, anyone know of some alternative power supply/stepper motor sources?

-Josh

[TOTALLYRC]

There is a supplier onn ebay that has toridial power supplies but I can't remember his name.

[ger21]

antek, I think.

[radcliffe]

http://stores.ebay.com/Antek-inc

Harold

[ahren]

Josh,
The design looks good. I'm not a big fan of mdf for uprights, even double glued the way you've drawn. If these flex, you can get racking in your system. I realize 8020 can be expensive, so my suggestion to save money would be to go with steel tube or plate for the uprights (you can get away with hot-rolled for this). Get it cut to length, but you can drill it with a good drill press and a starter punch and get a much more rigid connection than anything with mdf. Having priced out steel from various suppliers, it looks like speedy metals is one of the best values. That being said, snowgrains machine is working with mdf for the materials he's cutting, so it may work for you. You can always replace it with steel later.

Also, make sure you account for where your motors are going to mount, and where your bearing supports are going to go. Otherwise, go for it, and good luck with your build!


Ahren
www.cncrouterparts.com

[wizardrule]

if you notice on the gantry Ahren, it appears he has angle iron on the uprights. I think stiffness would be at premium with that set up.

[ahren]

I did notice the angle iron. This is a good idea, but is really only as strong as the method used to fasten the iron to the mdf. If these are just glued on, then I'm guessing the joint between the two materials will break long before the real benefit of the angle iron is reached. Then again, if the steel is bolted on, this might be a viable means of strengthening the setup.

Ahren
www.cncrouterparts.com

[wizardrule]

Agreed on the glueing for sure, but if fastened with screws it should be more then stiff enough to handle anything that gets cut.

[jwillhite]

Originally Posted by wizardrule Agreed on the glueing for sure, but if fastened with screws it should be more then stiff enough to handle anything that gets cut.

Yepp thats steel angle running up the sides of the gantry to help stiffen the mdf, I was planning on bolting straight through the angle and mdf into the ends of the 8020.

I'm no materials expert so I don't know exactly what to expect as far as deflection goes but it seems to me like that thickness of mdf combined with the steel angle should get the job done.

[jwillhite]

Originally Posted by ahren Josh, The design looks good. I'm not a big fan of mdf for uprights, even double glued the way you've drawn. If these flex, you can get racking in your system. I realize 8020 can be expensive, so my suggestion to save money would be to go with steel tube or plate for the uprights (you can get away with hot-rolled for this). Get it cut to length, but you can drill it with a good drill press and a starter punch and get a much more rigid connection than anything with mdf. Having priced out steel from various suppliers, it looks like speedy metals is one of the best values. That being said, snowgrains machine is working with mdf for the materials he's cutting, so it may work for you. You can always replace it with steel later. Also, make sure you account for where your motors are going to mount, and where your bearing supports are going to go. Otherwise, go for it, and good luck with your build! Ahren www.cncrouterparts.com

Ahren thanks for the advice, yeah the gantry vertical supports are definately a concern. I was thinking of glueing the mdf together then bolting through it and the angle iron to the 8020.

Yeah your right steel tubing or even plate would probably be preferable. I have some mdf and steel angle hanging around here though so I might try that first.

As far as the motor mounts go I need to play around with the model a little and make sure the geometry works out.