Aluminum Mechmate

[Jkountz]

I have been in the design and planning mode for so long now Im starting to wonder if I will ever actually build a CNC or not. I have spent a good amount of time over at the Mechmate site and while I really like the MM I hate the idea of proprietary parts and alot of welding, along with big heavy components to lug around.
So having studied a few excellent machine builds right here on CNCZone I decided to design an all aluminum, bolt together sorta/kinda version of a Mechmate. Actually its more Mechmate influenced I guess you could say since it wont in fact be a Mechmate at all but those familiar with Mechmates will notice the similarities. Most all the main components will be from .375" aluminum, regular stock easily found at most metal supply houses anywhere. Nothing has to be custom fabricated or bent and the weight will be significantly reduced. I have attached some pics of my initial design done in Sketchup for comments or suggestions.
The drive is all Rack and Pinion and right now I have about 7 inches under the Z. Im thinking of a 4x5 or even a 4x8 overall cutting capacity.
Tell me what you think please, and one more thing the name I put on it was just in fun!!
Jim

[Jkountz]

And a couple more pics. The double pinion gear on the Z drive is some sort of fluke in Sketchup that I Cant seem to delete for some reason. When I do it deletes the entire motor assembly. Also the two springs that tension the motor to the racks will also have the customary turnbuckles on them, I just didnt feel like drawing all that in!!
The last picture shows my thoughts for the X axis v rollers.

[DIYaholic]

Looks good Jim.
I too am in what seems to be an infinitely long research, planning and design stage. I was also considering a similar gantry design. Are you planning on or done any deflection calculations? I would be interested in the results, could you post them?
I'm not familiar with the mechmate plans/designs. I have registered at MM, but have not looked around yet. What technique will you use to grind/mill the angle for the v-rollers to ride upon? When do you think building will start? Are you planning a build log? I'm very interested in your design and will surely track your progress.
Good luck and keep us posted on your progress.

Randy

[Jkountz]

Well Randy I was going to go the scientific route for deflection calculations. Lay out two 2x4" aluminum tubes and start putting weight on them until I can measure significant deflection!! Kidding of course but I really dont know how to go about that actually.
As far as the rails I will either use the "skate" method the MM guys use or just have them milled by a local guy here. I considered buying the v rails but they are kind of costly, have to do some number comparison to see what way is best. For the Z axis I can mill that one here using a jig for my disc sander but it wouldnt work for long stock. Since that piece is only 16" long it will be good though.
I am going to keep a build log and I hope to start sometime in the next month or so.

[DIYaholic]

I haven't a real clue about deflection calculations either. I know 80/20 has a downloadable deflection calculator, but I don't know if it can be used for materials other than their extrusions. Perhaps the intellegent experts here can point us in the right direction (a link to formulas to calculate deflection). Depending upon what your machine will be used for, those calculations may not be important. I want the ability to cut/mill aluminum plate, so I'm going to have to figure out deflection prior to building.
Any way, remember to post updates and pictures, pictures and more pictures. Did I mention...pictures?
Randy

[Jkountz]

Also if anyone is interested I would be happy to send the Sketchup file for you to play with.

[DIYaholic]

I took another look at your Y gantry/Z car setup. Other than the Y pinion gear spring (which is only on one side), what is going to oppose the lifting forces to keep the Z car down on it's rails? I would run another set of V-rollers/angle rails on the underside of the Y gantry.
Just my $.02.

[Jkountz]

Good eye Randy, actually I will probably just use an idler bearing setup, again this idea from the MM design. Seems to work fine for holding down the Y. I will draw that in and post a picture of what Im talking about.

[DIYaholic]

I would be interested in the sketchup file, that is once you have your design "finalized". Are we ever finished designing/redesigning?

[alexlis3]

Its very good idea...

[Jkountz]

I have found an excellent deflection calculator online that can be found here---->
http://www.botlanta.org/converters/d...c/bending.html

According to it the deflection of only one of the main gantry beams is .05046 with 60 lbs allowance for the Z/Y car and using 2x4x.25 aluminum beams. Again this is for one so can I divide that by 2 to get the overall deflection or is it more complicated than that?
Even at .05046 thats pretty good and there will also be a piece of 1x2x.25 steel angle bolted to that (v rail) that would have to stiffen the aluminum beam up somewhat I would think. Does this make any sense?

[LeeWay]

My first machine was quite similar in looks to this gantry.
I used steel tube though. I did use aluminum on some parts too, so it's a combination machine.
It is a small router but is still going great. The basic design works very well really. You don't have much concern with the Z tilting front to back under cutting force like some lighter over under rail gantries.
The trade off is accessibility to the router.
I used two cam clamps and pop my router out for bit changes.
Works well.
Here is a link to that build that may give you some ideas on what to and not to do.

Cutty Shark I

Below my Z carriage, I used one double roller bearing and three delrin pads with eccentic adjustment. That too has worked well. V rollers with cam adjust would be a good choice too I think. Maybe a bit more precise.