My cnc hobby.

[wjbzone]

I am still adding to it. Need to get a better table top. Travel is 24 X 13 X 7. The Kress router is great. 6000 to 26000 rpm - very quiet.

Hobbycnc driver with 125 oz. in. steppers. Turbocnc. travel speed at 40 ipm with no problems.

Just wanted to show off one of my first programs...

Bill.

my web page

[JOE65]

Wow looks really great Bill

How did you machine your alum. plate?

[balsaman]

Very nice machine. Looks great and looks like it works great too!

Eric

[wjbzone]

Thanks Joe,
I did most of it on a Haas VF1.

I have access to the machine shop (where I work) on weekends for personal projects.

Bill

[boxwood]

Looks great Bill, I have a hobbycnc board and getting 22 ipm with 24v supply and 8 tpi screw, curious what you are using for power supply and lead screw
Ray

[wjbzone]

Ray,
I am using a 35VDC power supply.

The ballscrew is a 5/8 OD x 0.201 lead. McMaster Carr PN 5966K26. (cost $1.07/inch)

The ballscrews nuts MMC PN 5966K16 (cost $20.63 each)

Bill

[wjbzone]

I've seen some posts of the costs in different machinines.

Here is my break down:

Aluminum ($1.00/ pound at scrap yard) $105
motors / driver / wires $180
ballscrew $77
ballscrew nuts $62
drill rod (guides) $55
igus bearings $68
misc bolts $20
transformer $36
case $45
turbocnc software $20
kress router $437

TOTAL $1105

Plus the computer (that I already had. )

I don't know yet what I will spend on a table top. The lamanited insert for a kitchen table is working so far. Any suggestions?

I estimated about 200 hours work. (very rough estimate)

Bill

[anoel]

Have you measured your accuracy yet? That ballscrew+nut combo produces a really funky inch per step number (0.001015625) I think turboCNC only supports 7 decimal places. So over 120 revolutions you'll be off .0006". Simple contouring should not be a problem but I wonder if a part that requires a "lot" of back and forth movement across each axis (like a large 3D part) would end up being a little goofy with the error being additive over the course of the run. (Again not a problem for something like sign/decorative work but might pose a problem when trying to do precision machining.)

I just wondered because that particular screw and nut are so much cheaper than the rest of the ballscrews in that category. I'm just wondering if the accuracy trade off is signifigant over time to not consider it.

[wjbzone]

I thought the same thing about that screw when I first priced it. Why so cheap? I assumed it was rolled vs ground?

It does have an odd lead value (about 0.201 inch/rev), but If my thinking is right, any inaccuracy caused by a difference in actual lead vs the lead that Turbocnc is given, would not be cumulative. Parts would be scaled up or down by a constant factor.

I have only checked the repeatablility of multiple movements over a 2" distance. It repeats within .001. I think I will check my accuracy by boring holes near each limit and checking hole locations on a CMM at work.

If my accuracy is off 0.0006 over (0.201x120) 24" I would be very happy. I probably have more inaccuracy due to the drill rod I am using for guides.

That screw vs an acme thread seems to me to be a good choice.

Bill

[wjbzone]

I checked out my accuracy by boring holes in a piece of wood and checking location.

Hole 1 at 0,0 - origin
Hole 2 at 10,0 checked 9.996,0
Hole 3 at 14,0 checked 13.995,.0012
Hole 4 at 0,-1 checked .0008,-.9999
Hole 5 at 0,+1 checked -.0016,.9990


Looks like I am out about 0.004" over a 10" distance.

These holes were bored in a 1 x 4 piece of pine side clamped in a vice then checked next day held down by one strap clamp. Some of the error could be due to clamping and some due to humidity (a lot of that around here lately)

It would probably be a better check in a piece of plywood, but I am OK with these results.

Bill

[anoel]

4 thousandth's of an inch certainly does not suck. I'm running at about 8 thousandths tolerance right now. (I've not really dug into finding out where the error lies, but I'm pretty sure that the fact that my machine is not as rigid as it could be has a lot to do with it.

8 thousandths is enough for press fit parts to not fit together. (so therefore I've been avoiding dong them.)

[wjbzone]

I just got my router on/off hooked up to the computer M3/M5. I used a Crydom solid state relay (model D2440-10) that switches up to a 240Vac 40Amp output based on a 5vdc input. Cost about $24 at a local electronics store.

It works great. I have several programs that I have been watching the time so I could go switch the router off. Now I just progam a M5!!!

Thanks to Jeff (homecnc) for the inspiration in getting it working.

Bill