Auxiliary belt driven high speed spindle

[Russ Kaiser]

I am running a ZAY-45 cnc conversion done by Master CNC. The gear head is gutted with a belt driven spindle and VFD yielding a maximum spindle speed of around 4500 rpm. I should also note that the Z axis moves the quill, not the head.

For high speed work, Master CNC offers two high speed spindle options: an air drive spindle and a router motor. Both are more than I would like to spend. I think I can work out a router mount fairly easily, but I will lose a lot of working room between the head and table because even trim routers are fairly tall.

I was wondering if anyone has ever mounted a high speed spindle on a RF-45 clone using the existing spindle to drive a belt that in turn drives a secondary spindle? It should be pretty easy to get a speed multiplier of 4 and since my primary spindle motor is 2 HP, I should have plenty of power left for spinning those tiny bits.

I was thinking about using some micro timing belts with a stubby Foredom Carving hand piece to hold the bits. For mounting the equipment, I thought I could us a slip collar that grabs the quill.

Has anyone tried something similar to this?

[691175002]

Sounds like a surprisingly good idea, and I've never heard of it being done before.

There will be a lot of ways to get it wrong though, make sure the belt can take that kind of speed.

[hoss2006]

It's been done before, search youtube, you'll find some videos.
Hoss

[LUCKY13]

What about gutting a router and just using the spindle out of the router to build one? I find routers very cheap on craigslist and at the local pawnshop.


Jess

[Russ Kaiser]

I started thinking more closely about the layout of an auxiliary belt and I ran into a bit of a snag. The quill of my mill has a bit of a torque rotation along the axis of the spindle. I guess if it really bogs down in some material it can move axially as much as ten degrees.

This tendency to torque would mean that for an auxiliary spindle to stay accurate its axis would have to be exactly aligned with the axis of the existing spindle and quill. That design constraint would necessitate a jack shaft. The belt and timing pulley would transmit power from the existing spindle to the jack shaft and then from the jack shaft back to the new spindle.

The downside: another shaft, two additional bearings, two additional timing pulleys, a second belt, added complexity, and a loss of working height. When I factored all those items into it, the router looked better and better.

So...

I bought the Dewalt variable speed compact router DWP611. I ordered some aluminum flat bar for a permanent mount and made a proof-of-concept mount today using birch plywood. It's working fine even made from wood. Of course, the aluminum will help the router keep cool and be much stiffer.

The mount is grabbing the bottom of the quill. there is an iron bracket there that I moved up a bit. This required adjusting the z limit switches, but it left a 3/4 inch section to grab with the new bracket. I lost about 3/8 of an inch of z travel but I don't think it will be an issue. The height of the whole thing is a bit over 9 inches but I have plenty of Z adjustment left.

When I get the permanent mount done I will post a photo.

[Russ Kaiser]

Here are the photos of the mount that I made for the Dewalt router. It simply clamps to the bottom of the Mill's quill. If I had to do it all over again, I think I would have made everything but the clamp out of 1/2 inch aluminum. It's mostly 3/4 inch and a tad on the heavy side. It's also pretty poorly finished because I was using a very dull and long end mill to cut out the parts and I ran the parts at a "take no prisoners" feed speed.

I was surprised at how firmly the simple clamp mount works. I plan on giving it a shakedown cruise this weekend.

[doorknob]

That's an interesting approach that I had not considered - I don't (yet) have an RF-45 clone, but I had been thinking about possibly bolting an aux spindle to the side of the head (which would reduce the available table travel in the X direction, a downside which your approach does not have). I take it that your mount has adequate rigidity in the face of cutting forces?

[hoss2006]

That's an interesting approach that I had not considered - I don't (yet) have an RF-45 clone, but I had been thinking about possibly bolting an aux spindle to the side of the head (which would reduce the available table travel in the X direction, a downside which your approach does not have). I take it that your mount has adequate rigidity in the face of cutting forces?

Your x travel would still be the same with the aux spindle on the side.
The tables are long enough to shift your stock 3-? inches to the left/right from standard and still use your full x travel.
Hoss

[doorknob]

Your x travel would still be the same with the aux spindle on the side.
The tables are long enough to shift your stock 3-? inches to the left/right from standard and still use your full x travel.
Hoss

Useful info, thanks.

[Russ Kaiser]

Doorknob,

No testing as of yet but I jerked hard on it after I tightened the clamp and was happy with the sense of rigidity and the lack of deflection. If you think about the geometry you are adding quite a moment by extending the quill. When I am milling hard materials I will definitely be using the main spindle.

If you build something similar remember that because of axial rotation it's really important that the router spindle and main spindle are exactly aligned in the XY plane.

You also have to remember that in my particular application, my quill is my Z travel, not the headstock. If my entire headstock was the Z, I would have mounted it on the side.

My Zay has an extended Y bed so my milling envelope is 20.5 x 10.5 x 5. My Y travel is actually more than my table width by an inch. My headstock is supposedly at max height 18 inches off the table, but I can raise it to 20 without any issues. I still have have enough workable z height with the headstock raised to its max to use a long mill with my max Z travel.