Is a 31 inch diameter Indexer possible?

[richards]

One of the factors is the minimum distance per step. A machine that is optimized for a 6" diameter may not be able to preform properly with a 20" diameter or a 31" diameter.

When compared to a 6" diameter, a 31" diameter will have 5X more "coarseness".

If the indexer motor is geared properly to give you the required resolution, and if you have space enough to mount an indexer with a 31" diameter, you would get perfectly good results, assuming that your feed/speed/stepdown/stepover settings were correct.

[gerryv]

I think it comes down to the dia. of your piece times pi (3.14) to give you the circumference divided by the number of steps per rev. your motor takes. Therefore, 31" X 3.14 / 210 steps (a cheapie motor) = 0.46" "flats". Yuck. Thank goodness for micro-stepping, gearing and stepovers. Is this right?

That's not addressing some of the other influences already mentioned - I'm considering the forces in trying to accelerate and decelerate a 31" dia. x 10' chunk of hardwood (XXXX pounds?) through varying arcs - quickly. Wow, I'm guessing I'd worry about lost steps with an open loop setup. Just guessing though :-)

[Brady Watson]

You need a planetary or harmonic gearbox, or multi-stage belt box to have the correct resolution out at that diameter, with minimal backlash. You won't get, nor will you want, very high RPM if you free-wheel spin the indexer at that diameter. It can certainly be done, however you need the space & work for a machine like this, and unless the machine has a Y axis, you will be limited on toolpath strategies & versatility.

-B

[Mayo]

Gerald - this machine would be for styrofoam only - not a hardwood tree!

With a very low bed (if any) this machine wouldn't have to be any larger than a 4x8 shopbot - half the diameter is only going to be say, 16 to 18 inch. It would be taller but it would still fit in a normal garage or small shop.

[khalid]

Mayo..in this case your only limitations will be the tool length... your Z-axis bottom will strike to the work piece if you go deeper at some locations and shallower at other.. just imagine....

I personally want to make a machine that will only do Indexing.. The Y-gantry will be fixed to the machine base.. and centered on the center of chuck...

[myxpykalix]

khalid...like this one? Art and I along with a few others started the legacy yahoo group and from that machine he developed his first prototype (man was it ugly).
You are the europen version of McGyver, well hes the american version. Give him some hair pins, a little cardboard and chewing gum and he'll make you a cnc machine.


45632.jpg

[hfjim]

Folks,

I have a lathe/indexer I built with a 48" dia x 24' between centers cutting capacity. You can see it at www.hfmillwork.com. It was built with Minitec components and Shopbot controls.

Mayo,

If you're still looking for someone to cut those chess pieces, let me know.

Jim Turner
hfmillwork@bluefrog.com

[myxpykalix]

Jim,
That is an indexer on steroids!! I thought i understood that there would be problems with the "resolution" due to the size?
Do you have any other pictures or any youtube video?
Explain this if you can beccause i'm confused.
Since we are dealing in 360 degrees rotations if i have a 12" diameter column the length between each degree is not as far as if you have a 48" diameter column. If having a larger diameter is a problem how do you compensate for the difference in length between each degree?
Is the shopbot software you use to run your indexer modified in any way?
What kind of setup do you use for the actual cutting?
That is a VERY slick setup!

[khalid]

Jack.you need no worries.. If you have programmed the part for 11" then cut the part with 11" workpiece..the problem will only arises if you use the 11" toolpath to cut 31" part..

Just remember the above fact and you will have no trouble..

[hfjim]

Jack,

The indexer rotational stepper has a belt reduction of about 5:1 so it won't rotate very fast,but the resolution is fine. I do have another motor (variable speed) that I can use if I do more conventional lathe work. It also turns fairly slow (20-60 rpm. You can't turn these big columns very fast as balance is a big issue.