Bridgeport Spindle Encoder Design

[tblough]

Here is the spindle encoder I'm implementing on my Bridgeport clone. It will work in both direct drive and backgear and is 1:1 with the spindle. It is an invasive procedure and not and easy bolt-on solution. I will be using a RLS RLC2IC read head with a 50mm axial encoder ring.

My mill powers the quill and not the knee, which I think is the more common configuration. It uses the mounting points for the quill downfeed lever and the quill speed change selector to mount the Z-drive package, so the fine quill feed is inoperable and unneeded. This is where I will be installing my encoder.

The above photos are from my work mill with the Elrod quill drive. I'm copying this for my home mill which has a 2J variable speed head. Since the head is currently torn down to convert it to single speed sheaves, I'll add the spindle encoder at the same time.

The large bull gear mounts on the top of the Splined Gear Hub. The bottom of the hub has a 3-lead worm that drives the feed drive worm gear.

The Worm Gear Cradle and all of it's components including the miter gears and the cluster gear input shaft can be removed as their functionality has been replaced with the Z servo drive.

The wire from the encoder will pass through the hole for the cluster gear input shaft and the connector will mount on the bracket that replaces the range selector cover on the left side of the head.

[tblough]

This is the bottom of the gear housing removed from the 2J head. The photo shows the splined drive hub in the backgear position. It raises about 1/2 to disengage the bull gear, and engage the face splines on the top for direct drive. I will be mounting the axial encoder ring to the worm pinion and attaching the read head to the bearing carrier so that both move up and down together.

Here's the CAD model of the encoder ring and read head in the backgear position:

And in direct drive:

The read head will be encapsulated in epoxy after the wiring is soldered and the read head bracket attached. The read head bracket mounts with two 3mm SHCS through the side of the bearing sleeve. Axial clearance between the read head and encoder ring can be adjusted by moving the split clamp collar up or down.

I'm waiting for the encoder and ring to arrive. More photos to follow.

[tblough]

I had originally looked at a radial encoder because they have 90 poles vs the 72 on the axial rings. I wasn't real happy with the radial design because the read head extended past the OD of the bearing carrier. That wasn't a problem if the bearing carrier and bull gear were assembled into the bearing housing before the housing was attached to the head. The problem arose if the head were being disassemble following the various teardown videos on YouTube (here at 15:00) where the bull gear and bearing carrier were pulled out of the housing while the gear housing was still attached to the head. This would severely damage the read head.

By going with the axial setup, the bull gear could be removed as in the videos, but it will still be connected by the encoder wiring. A heavy hand could rip the encoder wiring, but hopefully that would be noticed before damage was done. The other reason I ended up with the axial configuration had to do with the bearing housing. For the radial configuration, I would have had to tap a series of M2 holes on the end of the bearing housing for the read head bracket. Unfortunately the bearing housing is heat treated and quite hard because it has the integral rack for the back gear selector. I was a little leery tapping M2 holes with a carbide tap, and much more confident of drilling and counterboring two holes with carbide endmills, so axial mounting it is.

The encoder ring and read head were less than $200 including DHL shipping from Eastern Europe. The read head was an RLC2IC with RS422 5V interface, 6-Bit (06B) interpolation, 1µs edge separation (C), no connector, with reference mark, and no special requirements. Actual part number was RLC2ICA06BC00A00. The encoder ring was an MR axial magnetic ring, 50mm OD, 2mm height, 40mm ID, with reference mark, 72 poles, stainless steel with back adhesion tape. Part number MR050C040A072B02.

[ScotY]

Hello Tom,
Looking forward to seeing this up and working!

[tblough]

Encoder is supposed to arrive on Friday. Hopefully there will be some progress this weekend!

[tblough]

The encoder arrived via DHL from RLS in Slovenia on Friday. Quality was excellent but I was expecting this from a division of Renishaw. I got it assembled to my mounting block, wired up, and potted.

Potted endcoder

The encoder ring was attached to the aluminum clamp ring I machined and assembled to the bull gear bearing mount.

Assembled to bull gear

The encoder cable was mounted with a cable clamp to the bull gear bearing housing as well to prevent any movement from switching between high-low ranges from reaching the soldered encoder connections. The green encoder cable continues to make a full turn around the front of the worm and then around behind the bearing housing when installed. This makes the cable act like a compression spring resulting in only a small amount of torsion in the cable when shifting between ranges.

end of bearing carrier

placed in housing

on 2J head

Finally the other end of the encoder cable was routed down through the now empty quill feed gear hole and out the quill feed speed selector location.

encoder connector

[tblough]

The connector gets mounted in a mounting plate for my quill drive that replaces the speed selector handle. I also mounted my work light to this new bracket.

Quill Drive Bracket

Here's the completed installation:

Z-Drive Finished

I'm waiting on the Capital Committee to approve the purchase of my Allin1DC, but I did hook the encoder up to my Oak board in my lathe to test the encoder out and got the expected counts and index pulses with no quadrature or differential errors!

[DICKEYBIRD]

Another great post I somehow overlooked until today. This is a very clever & tidy solution to the problem. Thanks for posting the great pictures & text. Another example of "Where there's a will there's a way!"

[ScotY]

Hey Tom,
Glad you got it all working! What does the encoder ring look like? I see a flat black ring on top of the split clamp looking part. How does it attach to the clamp?

[tblough]

The encoder ring is 1mm of rubber encapsulated magnetic media bonded to a 1mm stainless disc backing. That's what you get from RLS. You can order it with 3M VHB tape pre-attached or affix it with epoxy. I chose the VHB route - glass beaded and solvent cleaned my split clamp before bonding.