Bell-Everman Mini Polar CNC

[Mike Everman]

I've been waiting for something interesting to show on this, and tomorrow will be the first parts made with our Bell-Everman Mini Polar CNC.

The basic architecture is A, B, Z axes. "A" rotates the material, which has been bonded to a 6mm stud. The stud is placed in a 180 degree indexer, so that one side can be finished and then flipped to do the backside.

The "B" axis rotates the spindles, with twin spindles being an initial take on eliminating the future need for a tool changer that I will ultimately want.
We are using a Delta Tau Clipper control, so that all part data coming in as XYZ is automatically converted to ABZ polar coordinates. The video shows a test pattern, and I will have a part making video up soon.

I plan several material carrier styles, and am thinking toward watch making applications, where precious metal chips need careful collection.

The current design has two spindles with coolant sprayers. The spindles are 200,000 rpm air driven types, with 1/16" shank cutters, but they have recently been discontinued, so we are in search of a replacement. I may in fact be making our own, with an ER-8 collet extension as a beginning point. The approach I'm taking for spinning it up (again with air) has been breadboarded and reached 165,000 rpm, so almost there!

Video and more is at [nomedia="http://www.youtube.com/watch?v=LziQ4uTXhBg"]YouTube - Bell-Everman Polar CNC first pattern[/nomedia]
And more in the way of pics and write up on my blog: mikeeverman.com

Hope you guys like it! Almost ready for prime-time!

Any CNC control scheme would work if you don't mind doing the polar conversions at the CAM stage.

[veteq]

Hey Mike,

Long time no speak...
Thats some very nice machinery you got there, cool..!!!
Nice to see you are still making great machines, keeps me inspirated..!?

Myself still studying and having a blast at designing mills, got all the hardware know, (no compromises) and at the moment machining the parts at the university!!

Regards,

Roy B

[veteq]

Isn`t this a nice spindle replacement for it?
NSK America

The HTS ones..

[Mike Everman]

Too big. We could handle up to about a .75" straight shank at the rear for holding it.

[RomanLini]

Very nice setup Mike! Innovative use of dual rotary motion especially since it includes dual spindles as part of the bargain.

I also like the simplicity of your o-ring setup with simple plastic clamps over them allowing Z axis movement and rotation from the one seal.

Are you going to share more details (photos?) of the workings of the rotary drives? I'm assuming you went for toothed belts wrapped around the drums with 2 pinch rollers? Or did you go for the rigidity of worms and reduced speed?

One of my future machines will be a dedicated rotary machine (maybe 12" dia) to make cogs and wheels etc for hobby robot use.

[Jason3]

Very nice machine, Mike! I've been enjoying the posts on your blog, busting to see some more pictures and details Can I ask what cost ballpark the Delta Tau control is in? I've tried to put together something like this a couple of years ago and got stuck on the kinematics, being able to feed it regular XYZ code would be great. I wondered if you had considered and decided against DDR motors for the rotary axis?

Romanlini - Bell-everman Servobelt rotary drives Check out Mikes blog, there's some nice pics there. Bell Everman has more info and pictures too. Cool hardware!

Regards,

Jason

[Mike Everman]

Thanks much, guys! Seeing it go was a thrill to be sure.
We're not all the way there yet. The kinematic conversions are working well so far, and I'm working closely with delta tau toward am abbreviated nc front end, as we do not need a lot of the features in the standard package.

The clipper drive stack with control and integrated 8 amp continuous drives (going from memory) I think lists for about $3k.

As to ddr's, yes, ultimately the superfine version of this will be direct drive, direct reading encoders, but this style is quite good for the dollar at this point.

The rotaries are belt drive and only 5:1, so plenty of speed available. It was designed for 2g continuous accelerations minimum, which we are exceeding by a bunch. The z is a servonut lowboy stage with rotary encoder to save cost.
This unit can have renishaw direct feedback added on all axes, but that's a fairly expensive option most would not need.

[Jason3]

Hard to get a good idea how small the machine is without much visual scale reference - it looks fast in the videos! What is the actual feed rate we are seeing there?

The Delta Tau gear is quite reasonably priced - I was hopeful, but not expectant. Would you have a recommendation for a lower cost large bore rotary encoder for a DDR axis? I've ordered a Renishaw LM13 magnetic ring encoder, but wondered whether there was anything else worth considering? 2" bore would be nice...

Great work, looking forward to any updates

Kind regards,

Jason

[Mike Everman]

RSF and Numerik Jena (sp?) have some good reflective ring encoders. Heidenhain i thought was going to make a circluar band for their tape heads, but I haven't been following them.
Yeah, I have a few of the renishaw magnetic tape encoders I haven't tried yet. They have a rather large magnetic pitch spacing, so shortwave errors are high, but good enough for machining, I think.
My products use the 200 and 75mm ring encoders, which are expensive.
Were I doing a DIY encoder, I'd get a codewheel printed or attempt it on a laser printer, and use a USDigital HEDS reader.

The mini CNC spuds on which the material indexer and spindles are mounted, is 3.5" dia for scale. The whole thing is 15" wide.

[Jason3]

Thank you Mike, that is very helpful. I took a look at those, the Numerik Jena ones might be particularly nice if there was very limited height available. I'm a little concerned about potential error with the magnetic ones, nearly went for the optical but the cost is so much lower I kind of have to try the magnetic one and see. The response when I asked about the optical one was very delicately put - "...if an application is expecting a low cost solution then our RESM/Tonic is not appropriate to consider" Ha

That A axis is a neat unit. Is it an in-house product? 180º index only? <= ah, dumb question, sorry. I read the first post again...

Kind regards,

Jason