Need Help!- Going to order screws tomorrow...

[SatanKlawz]

I am going to order my screws tomorrow from mcmaster. I just wanted to run it down again and make sure I am making the right decision. My 3 axis router is going to use the g540 that I have already purchased and it will be turning the recommended steppers from keling. My 2 horizontal axis are 60" x 30".

Should I go with 1/2-8, 2 start, 4 turns per inch.

or... 1/2-10, 5 start 2 turns per inch.

[BobF]

Either one will work.
I would choose the 5 start, 2tpi now because I have the others now and think the 5 start would take better advantage of the torque available at lower stepper speeds. My motors and drivers are HobbyCNC 305 oz/in.

[arizonavideo]

Get the faster screws like 2 TPI and buy them from Roton.

http://www.roton.com/Mating_Componen...mber=60986&#PN

I have yet to hear someone say my machine is too fast...

[SatanKlawz]

Are the screws @ roton better than the precision acme screws that mcmaster sells? Also, are the roton Hi-Lead screws just another way of saying that they are fast travel multiple start?

[ahren]

The 2 TPI and 5 start 1/2-10 should be equivalent in terms of speed -- they're saying the same thing, although they may accomplish it differently (for example, you could get 2 TPI with a 1/2-8 4 start). I'd personally go with the McMaster screws, as nuts are readily available from them, myself, and Dumpster CNC.

Ahren
www.cncrouterparts.com

[rlwoodjr]

Originally Posted by ahren The 2 TPI and 5 start 1/2-10 should be equivalent in terms of speed -- they're saying the same thing, although they may accomplish it differently (for example, you could get 2 TPI with a 1/2-8 4 start). I'd personally go with the McMaster screws, as nuts are readily available from them, myself, and Dumpster CNC. Ahren www.cncrouterparts.com

Is anyone making taps out of a piece of the 2 TPI rod? I did this with the 5/8 -8 single start with UHMWPE, but was curious if it has been done with a multiple start.

[ahren]

It is doable, but the taps are very difficult to use with this high of a helix -- they take an extraordinary amount of force to push through, since the tap doesn't want to pull itself through a half inch in a single rotation. In order to make it work, you need to cut a much larger minor diameter than the actual thread just to have a chance at it.

I cut my multi-start ACME nuts on high-end cnc equipment in multiple passes. I tried making some custom taps, and all of them seemed to bog down fairly quickly. A custom combination roughing / finishing tap always seemed to be quoted north of $1000, so I had to find another way to do it. My method involves custom tooling and 5 helically interpolated passes with a thread cutter.

Ahren
www.cncrouterparts.com

[arizonavideo]

The guy I talked to the other day at Roton says they make the rods for McMasters.

They cost less at Roton too.

I keep seeing people go with slow screws like 10 TPI and then use some high inductance steppers and then they just cant get any speed.

The slowest screw for most people for the X and Y should be about 4 TPI.

[rlwoodjr]

Originally Posted by ahren It is doable, but the taps are very difficult to use with this high of a helix -- they take an extraordinary amount of force to push through, since the tap doesn't want to pull itself through a half inch in a single rotation. In order to make it work, you need to cut a much larger minor diameter than the actual thread just to have a chance at it. I cut my multi-start ACME nuts on high-end cnc equipment in multiple passes. I tried making some custom taps, and all of them seemed to bog down fairly quickly. A custom combination roughing / finishing tap always seemed to be quoted north of $1000, so I had to find another way to do it. My method involves custom tooling and 5 helically interpolated passes with a thread cutter. Ahren www.cncrouterparts.com

I have an old Logan lathe. I was playing with the gear ratio and I can get 1/2" of Z for 1 rotation of the chuck. I would have to turn the z thread by hand but it seems doable.

I was going to buy a short piece from Roton, but they have a $60 minimum...Anyone have a short piece they want to send me?

[ahren]

I can send you a short piece of 5 start if you pay for shipping -- just PM me your address and we can work it out. I'll be interested to see what you come up with!

What are you planning to use for a cutter? ACME threads are not triangular, you know.

Ahren
www.cncrouterparts.com