[Greenbuggy]

Hey guys, as I'm plotting out this CNC upgrade course with my old Lagun FTV-3, I'm trying to figure out creative ways to get the most bang for my buck.

The servos currently on the mill are old Electro-Crafts complete with toothed-belt driven tach/resolver feedback, drives are gone and my plan is for a new power supply and Gecko G320-X drivers. For starters I want to upgrade the quill to make sure I have this whole gecko drive and control system working and understood and then apply the same lessons to the remaining axis'.

That said I have a HEDS 5500 encoder I bought off ebay that takes a 3/16" shaft, the ballscrew out of the quill housing is 1/2" and so is the motor shaft that drives it via a belt. I don't mind buying a different encoder but have had a hard time finding anything that has a 1/2" bore for a reasonable (Say, <$200) amount of money. On the X/Y axis I can turn down the shaft sticking out of the back of the motor to fit these encoders fairly easily, but the quill motor only has a single shaft. I do have extra 1/2" shaft above the pulley I could attach something to or turn down, so really what I'm looking for is guidance on what the best way to do this would be. My options as I see them:

- Turn down shaft above pulley on motor, affix encoder via brackets
- Turn down shaft above pulley on ballscrew, affix encoder via brackets
- Drill either shaft and press in a pin to drive encoder, above pulleys
- Drill backside of motor housing, drill shaft of motor, press in pin, affix encoder to motor housing
- Get a 1/2" bore encoder, affix to motor shaft or ballscrew shaft

I would be open to 1/2" bore encoder options that aren't too expensive. I did find an accu-coder one on ebay that says 100 CPR which seems really low to me for a reasonable price - Am I correct in assuming so when the cheapo HEDS encoder is 200 for less than half the cost? How much accuracy am I sacrificing with a 5 TPI ballscrew?

There are other shaft-driven options too, mostly Dynapar brand and again more money, is there any problem with coupling this to the 1/2" motor or ballscrew shaft with a cheap ebay "CNC motor shaft coupler"?

Otherwise I'd like to hear what you think the best option is and especially why. Pics of what this is going on can be found here:
CNC Mill | Facebook

thanks for the help

[Bubba]

On one of my servo motors, I chucked it up in the lathe and drilled a ~1/4" (I think) hole in the back end of the servo shaft. Cleaned the hole real good and loctited a piece of drill rod in. Been that way for over 10 years now and works fine.
On my Z axis servo, there was a threaded hole in the end of the main shaft. I screwed an appropriate socket headed set screw in and made an adapter of the correct size to screw onto that. (I needed to put the encoder on that end as there was not enough clearance on the back end)


Also, my X axis encoder is on the Ball screw and the Y axis is on the servo. Again, both work very well.

[Al_The_Man]

If you go the threaded pin route as Art suggests, I would use shoulder bolts, as there is less likelihood of eccentricity and run out.
The other option is to fit a bracket and use a shaft coupler instead of a through shaft.
e.g. ebay 180882602191
If going with Mach you may be limited to a maximum resolution.
Al.

[Joe NH]

US Digital has some through bore encoders up to 1" diameter with up to 2500 CPR disks, for about for around $100. I am going to try them on my Bridgeport upgrade.
Joe

[mike_Kilroy]

sounds like spending yet more money on another encoder (s?) plus machining and time making it fit, maybe not centered, etc....... so another alternative..... a RESOLVER feedback drive instead and use motor (s?) as is??

I know the Gecko is low cost, but so are a lot of resolver based drives still today...... might be cost is same or less overall to new Gecko/encoders/machining...... but just an idea.

or get a resolver->encoder converter board instead and KISS?

If you want example costs, PM me (include motor volt/current/dc-or-ac) and I will send u part nos, weblinks to manuals, etc, for some choices......