Official Luthiers Forum!

Ed I use a very similiar design of bearings mounted on aluminum angle that run on black pipe for the sliding sled on my re-saw. It works good but drilling those holes for the bearing bolts needs to be VERY accurate. For resawing split billits it is not as crucial as for a cnc machine, but even still I had to slightly slot a couple of holes to make sure that all four bearings were...bearing.

Shane

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Canada

[QUOTE=Anthony Z] Lance/Brock if some of the contributors to this thread start building machines would you folks considering running a separate CNC Thread as you have for the Charity Guitar, Michigan Luthiers, etc.?   [/QUOTE]

Sure. I think there is a lot of interest in this.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

I agree with Craig. This is something you want to last. I built my sliding table out of MDF but I will soon change to hydraulics so it was never meant to be permanent. I built my fox bender out of baltic birch because I want it to last and I want it to look very nice when my customers come in to the shop. I think that Baltic birch is probably stronger, lighter and more stable. I might though make the table out of MDF for the smoothness, mass and cheap replacement cost if you start cutting into it.

Shane

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Canada

Thanks for the input. Jim I will really make sure that the square tubing is straight, also I'm going to buy posts with a flange on one end bolt it securely and make the other end adjustable. I will probaby make the length of the tube adjustable by using a bolt system like those neck jigs.

Shane thanks for the heads up on the skate bearing mounting.

I've decided to go ahead and go with the Baltic
Birch for this project since that seems like the consensus here, I think it will be pretty to.

I also agree with Anthony, I know learning how to use cad/cam software will be an uphill battle but i'm confident I can do it. Anthony thanks for the links, one big problem I see with a factory built machine is the cost, granted being able to by a nice sturdy machine for about 3500 is a great bargain but how many of us have that kind of cash to spend all at once. By building it yourself you can work on it at your own pace, buy what you need a little at a time as the cash flow allows. If I wanted to I could even build it out of aluminum (Brock where is the spell check?) I decided I want to go with birch to prove that anyone can build a decent machine at a low cost. I'm sure that after I build this machine I'll then use this machine to make the part for my next machine out of aluminum, thats what most people on the cnc forum do.

One more thing, there is lots of help and support on the cnc forum just like it is here. Many newbies are getting help understanding cnc and programing. So i feel if I get stuck somewhere along the line I'll have many friends come to my aide just like it is here at "home".

Well I picked up my lumber but there was a problem, I could not find baltic birch in 3/4 just 1/5 and what was available didn't look to good. I talked to one of my friend in the construction business and he told me i should use a product called Extira, he says it's a lot more stable than either the birch or the MDF. I then went to back to the lumber yard and they showed me a test they had done with this stuff. They put a long piece of this and MDF and assorted plywood including baltic birch submerged in water for 2 weeks and this stuff hardly looked different then when it was new. some of the other products had started to disintergrate. The birch held up pretty good considering the conditions but it had a big bend in it. After that I was convince to go with this new product. It looks just like MDF and costs around $45 a 3/4" x 4' x 8' sheet. Once I start building I'll post pictures.

Ed, another option, though heavier (which might actually be good), would be to use corian. You can pick it up for a reasonalble price on ebay. You could also consider propylene.

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Don Atwood
Arlington, VA

Don, I did think about corian in the begining but it was cost prohibitive. Today I started laying out the design on this extira material, I like it, there are many good things said about it on the web.

Is it done yet, Ed?
Are we there yet?

I wish it was done Nelson. Actually, today I started cutting out the parts. I cut out the section for the table and the gantry, when I get the gantry together I'll start posting some pictures. I'm trying to decide whether I want to buy the 3 axis kit or the 4 for the future. 3 axis electronics kit is $350 minus the box for the components, 4 axis about $100 more.

Ed--My experience with the 4th axis is that you can "borrow" one of the three drives temporarily if you want to drive a rotary or "A" axis. I say this because normally if you're doing rotary axis work, either X or Y will stay on centerline of the rotary axis. This depends, of course, on which axis the rotary cl is parallel with.   So it's a matter of switching the unused axis drive cable temporarily to the rotary axis.
You may even want to "borrow" the stepper motor itself from the unused axis and mount on the rotary axis to save buying a 4th stepper. I'm assuming that you would not be doing a lot of switching back and forth between 3 and 4 axis work.
Nelson

Thats a great idea Nelson! I'm sure I could setup the steppers so that they could easily be changed out.

Ed--I probably should backpedal a little here and quality my statements above. I'm assuming that Mach3 will let you reconfigure the pin outputs.
Nelson

Nelson, I'll look into it.

Ed--I think worst case scenario is that you would have to do an edit/replace in your Gcode if your CAM insists on outputting an "A" axis prefix instead of X or Y.

Nelson

Nelson,
are running an open loop system or closed loop, and if open loop have you had any problems with it?
Thanks

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Jim Watts
http://jameswattsguitars.com

Jim--I started out several years back running open loop with underpowered steppers. Had plenty problems losing steps and/or stalling out. This was with 70 oz.in steppers (very tiny) on a Maxnc10. I retrofitted with closed loop servo drives and it is now a much better machine.
Also retrofitted my Techno-Isel router with servo drives. It was extremely noisy with steppers and I think it was due to harmonics generated along with the lightweight construction of the Techno-Isel.
With that said, there are much better stepper drivers on the market now and I think that the key is to not be unpowered.
Nelson

So Nelson, I found this place called www.homeshopcnc.com that has 640 oz/in steppers for about $100 each and gecko drive for another 100. Do you think these would be big enough? Do you think you need as big a motor an the Z axis as the X & Y?
I think maybe I get too hung up on all the industrial stuff I work with and question weather you can really do this (make a cnc that works well) as I see many have and I just need to take the plunge, so to speak.

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Jim Watts
http://jameswattsguitars.com

Jim--I believe the 640 oz/in would be plenty healthy as this size is used on Bridgeport vertical mill retrofits. I believe most guys use a smaller motor on the Z. An advantage of steppers over servos on the Z axis is that a stepper will tend to hold position better with power off because of the permanent magnetism in the motor.   I use a constant force spring on the Z on my router (servo) to hold position (ballscrew) in the event of power loss. Learned this the hard way.
I use Gecko drives and have no problems. They've become the De Facto standard for retrofits.
I believe you could get by with much smaller than 640 oz/in for a CNC router but better overpowered than underpowered. (Until you have a crash)

An improvement that I would like to make on my CNC router is a tilting head fore/aft and possibly even sideways. Doing contour cutting with a ball nose endmill (round nose or core box cutter?) produces a scalloped surface but it also leaves a compressed line of wood under the centerline of the cutter. This "telegraphing" as I've heard it referred to, has to be sanded out and is more pronounced on the softer woods such as spruce. The cause of the compression is the zero surface speed at the centerline of the router spindle. The wood is being "bulldozed off" at this point rather than sheared. This is true, of course, with any cutter or bit that has to cut all the way to the center.
I figure that being able to tilt the head (router)just a few degrees would eliminate this conundrum (sp?)by moving the bit centerline away from the finish cut surface. The cut surface would be generated by a diameter on the ball nose that would at least have a little bit of cutting speed. (SFPM)
Hope I'm not talking to myself here.   Would enjoy hearing some opinions and suggestions on the above.
Thanks
Nelson

Nelson, wouldn't those changes be equivalent to a 5 axis machine? would mach2 or mach3 be able to control additional axis's?

Ed--Interesting question in that the additional joint would in fact constitute a 4th or 5th axis. I would probably avoid the complexity, however, by keeping the tilt adjustment manual.
I might mention, just as a point of interest, that my first CNC router consisted of a shopbuilt large faceplate lathe with a stepper connected to the spindle with a small roller chain and sprocket arrangement. Then used the slides off of the Maxnc10 for the X and Y (vertical) axes. Actually cut the 3/4" MDF pieces mounted to the faceplate to make my archtop body mold.
Programming was interesting in that what would normally be X & Y cartesian coordinates had to be converted to polar coordinates. It was a head scratcher.
Nelson

Here are some picture of what I've don so far. Here is a picture of the gantry without the bridge and with the lower torsion box minus it's cover.



Here is a picture of the bridge torsion box under construction.



bridge section complete.

Heres a picture of a test fit of the upper bridge rail.



And finally a couple of pictures of the bridge being test fitted on the gantry.

Now I have to wait on the bearings and rod before I can do more. Everything so far is level and square. Also, the sides seem to be very rigid but I still might add some stiffeners for good measure. Right now I'm going to seal everything and paint it with a nice arcrylic enamel. If you see an area that I can improve on as I go along feel free to give constructive criticism.