First off, I need some help. I bought an 80/20 CNC frame with THK bearings which is 20" x 20" x 9". I plan on expanding it to 3 x 3 and lowering the Z axis quit a bit (Mark's suggestion). I am building this bit by bit and what I'd like to do with it is at least be able to cut 1/4" MDF and other hardwoods as well as do some carving. I am only familar with my Phlatprinter, as far as CNC goes and I could use some advice as to what size (oz/in) stepper motors I should be on the look-out for?

I have an extra EZcnc controller and 3 of the Vextra/Vexta? motors laid back for my when I get it but I am thinking maybe they are to small? Yes/no?

All help is appreciated and If you have any stepper motors that you think may work for me, please contact me. Attached files

 

Buk you may want to look into a kit like this one to run this machine
http://www.probotix.com/3_axis_stepper_ ... river_kit/
Its from the probotix company and looks like it would serve your purpose. You could still use the USBCNC board as well.
Good luck with the build
Mark and Trish

 

Thanks Mark, that kit comes with 260 oz/in motors, I was guessing that I would need much bigger steppers, this is good to know.

 

I think that 260 would be good, but it really comes down to how fast and deep you want to cut in a single pass. Then you have to take into consideration that even if you put a 1000oz stepper on there will the machine deflect when you try to make hogging deep cuts and defeat the purpose? I am guessing it would. Randy told me once that at his shop they have giant mills with gantry's that are something like 2" thick steel structures and they still see deflection if they try to cut too deep or too fast. And their shop has started to do high speeds with little depth cuts to save on the machine life and eliminate deflection. So there is a trade off and these situations. I would say that 260 oz steppers would be perfect and I would not spend the money to go much bigger. :02cents:
Hope this helps and you may want to talk to Randy about this too he has seen it in action in his shop and since he told me that story, pretty much everyone I know who has a machine shop has told me the same thing.
Mark and Trish

 

Thanks alot Mark, that sounds like good advice. It makes perfect sense too.

 

I think those 260 oz steppers would work good too. I bought some of their 200 oz steppers(they don't stock now) way back for my MK1 and was pleased with the company. I had to contact them recently requesting specs for the steppers and they responded very quick.

Nice looking setup Buk.

 

I can see how it could rack with just one if you use a single bearing like they have, on the Y table. You may get away with cutting light duty media but anything heavy may rack the gantry. I think with the bearings being the type they are you may get away with it because they are linear and because of this have a little bit of that spacing built into the rectangle design but very little and that is not the way they are intended to be used.I think it could still work using a slave motor so you run two steppers on the Y table axis but that does not see worth it and would be like putting a band aid on the problem. Krokos right and that's really not the solution, your best be would be to add sides to this gantry with some spacing between the bearings. You will lose some of your travel but it will become a much sturdier machine.
Here is a pic showing the spaced bearings idea


Good eye Kroko! Sorry I missed this Buk, I was thinking steppers
With a little work you have the makings of a nice machine. Just need to find more of those same bearings to make it happen.
Out of curiosity when you push on the X carriage to move the Y table axis does it move OK? Even if you push from the right or left side and not center?
Mark and Trish

 

Great tip! thank you for sharing this
Mark and Trish

 

Maybe I'm not understanding..? There are 2 bearings, one on each side, that carries the X axis, 2 bearing blocks, one at top and one at bottom, which carries the Y gantry and the Z axis is on 2 cylindrical tubes/guides which may have bearings, I cannot tell without taking it apart.

All axis move very smooth and free regardless of where I push them, left, right, top or bottom. Should I be looking for more movement parts?

 

I am appreciating the help very much. I see your point.

I included some pics. Pic #1 is my current X axis (just an example) bearing and rail on the left side.
Are you suggestion the configuration in Pic #2? I assume you are, or the configuration in Pic #3? I only bring up Pic #3 because my framing is double thick (2") on all the bottom frame and has room for a top and bottom bearing rail for the X axis.

 

Hey Buk,
I think what Andrej is recommending is what is shown in the top of the pic I have here. What you have right now is shown in the bottom of the pic.

2 bearing blocks on one rail would be better, but then you would need to redesign what you have and try to find the same bearing blocks to fit your rails. Attached files

 

OK, I see... So I guess I'll be on the look-out for some more bearing blocks.

Thanks guys

 

Just make sure they are the right ones for your rails. Not all bearing blocks and rails are the same.

 

How do you measure and determine what is needed? Measure the rail face?

I know the bearing profile will have to be the same (V groove, U groove, etc.) but is the measurement I am showing correct for determining the proper bearimg size? Attached files

 

That I'm not sure of. Maybe someone else here will know.

 

Buk,
Can you get one off to see who the manufacture is and maybe a series number? It would be a lot easier to get this way, usually the rail system is what goes with the bearing, so they need to be from the same co. You can look here http://www.technico.com/thk-lm-guides/info_23.html and maybe call these guys to see if there is a cheaper alternative to THKs.
Hope this helps
Mark and Trish

 

That's a nice one Yoram, it gives you all the areas needed to measure.
Not sure if you can find them cheaper but some of the stuff from mcmaster you end up paying through the nose for. One of those blocks was $352.73! and even at the cheaper ones $100 a bearing your looking at a over a grand in bearings alone to start a machine like this and that's without even getting the rail! but boy are they nice!
On a good note, It wont be to to bad for you Buk because you only need a few of the bearings if you go this route.
Mark and Trish

 

Yea, nice Mark but too expensive for me. I contacted the guy I got the stuff from and lucky for me he has (4) NIB bearing blocks that match the ones I have that he is selling me really cheap. So on to the next hurdle...

 

Good to hear!
Now its just a matter of making up new bearing blocks to fit two of them(remember to use the 2:1 Rule that Kroko posted)
The only issue with doing it this way means you will lose some of your work area but it will be a nice strong mill.
Good luck with her
Mark and Trish