Shaft Diameter, LeadScrew Diameter, Motor Torque?

[cnc-newb]

i am wanting to build a fixed gantry 3axis machine. it will be small with a working area of 15x15x6-7". i understand that the bearing, leadscrews and support shafts w/ be expensive but i want this machine to have the ability to cut some decent Al - 6061 or 7075-t6 or so.

i was thinking the machine will be made out of 6061-t6 Al - 1" thick if that will work (have a friend that owns an industrial cnc machine shop so after i give him drawings he can cut the parts out for me, so precision will be in from the beginning).

what diameter shafts should i use? same w/ leadscrews? also, how much torque per axis is needed?

when i say i want to be able to cut Al, it doesn't need to be done fast, just accurate to ~+/-.010" or better if possible.

will probably start off using a trimmer router as the cutting device for the beginning.

i have been reading a ton and another question i had was -
are the end shaft supports needed or could i have the holes cut say 1/2" into the alumimun sides for the supports? or should the base be say 1" aluminum (w/ cleanup cuts on both sides to make sure it is 100% flat) and then the end shaft supports be mounted to that?

should the lowest axis have 4 support shafts or two supported support shafts if i do the large Al base?

thanks in advance,
newb

[ger21]

1) The linear shafts need to be fully supported along their length.
2) A laminate trimmer isn't going to work for cutting aluminum. You'll need something that spins slower and has more power.

[ViperTX]

I was going to send you to campbelldesigns.com , but looks like he has removed / hidden all his moving table router design stuff.

Anyway...cutting aluminum with a CNC router of your design....well power and rigidity are definitely key. Personally, you will spends thousands of dollars on the CNC router and you will be disappointed with the cut on aluminum unless you're happy with taking off 0.001 inches at a time.

Whenever you cut any material there is always some torque reflected back into your system, this is where the mass and rigidity of your system is important. I use a Jet JMD 18 to mill aluminum and it does an okay job. do the same job on a Bridgeport or VMC and there is a big difference in the quality of the cut. Do the same job on a homebuilt CNC router and depending on the design the quality of the cut will range from unacceptable to okay.

Good luck and keep us posted on your efforts.

Check out 5bears.com for a small home built CNC mill for additional ideas. Look at the Techno-Isel and DataCut sites for additional ideas.

[cnc-newb]

thanks for the info....kind of a bummer but definitely understand and thanks for being honest. if i were to take cutting Al out of the equation and just cut carbon fiber and/or delrin would that be a more attainable reality? also, i can get the machine made out of basically any normal metal (i was dong Al due to keeping weight low, but that may be working against me) - would some type of steel be better for the skeleton and gantry since it would ad more mass and leave the table and z axis Al? also, what type of steel and Al would be the best? is 7075-t6 that much better than 6061-t6 for a table? i have read the material differences but how do they correlate to real world usages of this type? or are we talking i just need a much larger machine?

the parts i would like to make will be used for 1/18-1/8 scale rc cars and they are designs i have in my head but also understand that revisions will be needed so 1 off are kind of needed, plus the fact that i would like to learn the cnc process is my reason for doing this.

again, thanks for taking the time to answer my newb questions

[cnc-newb]

if anybody could answer my last statement i would greatly appreciate it.

thanks in advance,
newb

[cnc-newb]

anybody??

[ger21]

I wasn't exactly sure which last statement you meant.

[cnc-newb]

sorry, basically shaft diameter and lead/ball screw diameter. i am assuming the thicker the better for obvious reasons but i don't want to get 1" when 1/2" or even 1/4" on the screw would suffice...

also, how much torque per axis?

last, should it be made w/ 6061, 7075 or some type of steel?

thanks in advance

[ger21]

There are calculations for the shaft diameter that will tell you how much they will flex. Google beamboy I think. For screw diameter, go to www.nookind.com and look at their column load charts which will tell you how much force you can apply for a given diameter. How much torque depends on how much weight your moving, how fast you want to go, how fast you want to accelerate, how much force you need, screw lead, gearing....... Lots of variables involved. Most motor manufacturers have motor size calculators that let you plug in numbers and they'll tel you what size you need. Or you can just use around 300oz motors like just about everyone else does.