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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > Servos for old Haas retrofit
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  1. #1

    Servos for old Haas retrofit

    I’ve got a ‘93 VF-1 I’m retrofitting. I’ve been looking at DMM’s DHTA15 servos, which are 1.3kw and Nema 42 frame, for all 3 axis. I think the shaft size and length would let me re-use the old flex couplers and having all 3 the same would make things simpler. I’m pretty sure this vintage machine used the same E728 dc servos for all axis. Do these servos sound reasonable for a machine like this? I’m thinking that if anything, they are a bit larger in capacity than the OEM drives. I haven’t had any luck at all finding the specs on the old servos though..

  2. #2

    Re: Servos for old Haas retrofit

    Sounds like a good choice of servos, I've used DMM servos on a couple of builds an have been happy with them.

    You can find the specs of the 728's here https://www.cnczone.com/forums/servo...tml#post183844 Al_The_Man has uploaded a PDF there.

    The DMM 1.3KW servos have about twice the rated torque of the 728's so no problem there. It's easy to turn the torque down on a servo, but pretty hard to get more torque out of an underpowered servo. Go Big or Go Home

    You may need a brake on the Z axis to keep it from dropping when not powered.

    I'll be interested on your progress on this build.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: Servos for old Haas retrofit

    You may need a brake on the Z axis to keep it from dropping when not powered.
    Does that VF-1 have a counterweight or spring setup to help offset the weight of the head? If not; you might consider adding one, if there is room.

    I'll be interested on your progress on this build.
    Me too...


  4. #4

    Re: Servos for old Haas retrofit

    That looks like them. Goofy 3.4” bolt pattern and all. Thank you.

    These old ones have a huge counterweight/chain arrangement that makes the spindle stay put with no motor attached. I only know that because mine has no motor attached. I can raise the spindle by grabbing the end of the flex coupler and twisting, but it doesn’t go anywhere on it’s own. I think the later ones relied on a brake in lieu of the weights or gas pistons (I think).

    I can’t find the A15 motors on the store part of the site so I emailed them. The fatter DST ones could be made to work just fine I’m sure, but the flex couplers are about $300 each so I’d prefer to reuse them (5/8 to 5/8 shaft vs 22mm).

    I’ll start a thread once I really get moving on it. One other small project I promised my wife I’d finish up before I tear into this one. At least I had the foresight to put the thing in her parking spot in the garage (she’ll be begging me to get on it once it’s cold

  5. #5

    Re: Servos for old Haas retrofit

    It might be easier to replace the couplers than try to find the 5/8 shaft motor. I don't think that is a standard motor.

    Here is what I am using for couplers, not cheap, but not $300 either.

    https://www.automationdirect.com/adc...ervo_couplings

    https://www.automationdirect.com/adc.../bore_reducers

    Good luck on your other project. Gotta keep the wife happy.
    Jim Dawson
    Sandy, Oregon, USA

  6. #6

    Re: Servos for old Haas retrofit

    I looked at those couplers the other day and dismissed them not realizing they had a whole slew of bore reducers available. That’s just what I’d need.

    I’ll wait any see if the DHT motors are still available. The largest one shown is a Nema 42 frame with a 5/8 shaft on it that’s just the right length to fit on top of a 1/2” or so thick adapter plate.

    I told her I wouldn’t start working on it but I didn’t say anything about buying parts for it.

    ETA: DMM emailed me back yesterday and said the DHT series servos I’m looking at are new and just haven’t been added to the store yet. I’m going to go with them I think.

  7. #7

    Re: Servos for old Haas retrofit

    Looks like I've hit a bit of a snag with the servo replacement. I took some measurements and the DMM servos aren't even close to fitting on the x-axis. I didn't realize how close the bottom of the table comes to the motor mount, but then the connector dimensions on those motors is the real deal breaker. Over six inches off of the centerline where I've only got room for about 3. I'll keep looking. It would be a bummer to have to put DC servos back on this thing.

  8. #8
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    Re: Servos for old Haas retrofit

    Couldn't hurt to ask DMM if they have a low profile option. Alternatively, I found this (somewhat pricey) Yaskawa 1.3KW servo on eBay that may work as it has the cables exiting the motors axially with the connectors on the cables themselves rather than the motor:

    https://www.ebay.com/itm/121559947732

    Just out of curiosity, did you get the VF-1 from around Rolla?

  9. #9

    Re: Servos for old Haas retrofit

    Quote Originally Posted by seanano View Post

    Just out of curiosity, did you get the VF-1 from around Rolla?
    That's the one.

    I emailed a couple of vendors to see if there are any lower profile options. There isn't much more room around the y-axis mount either.

  10. #10
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    Re: Servos for old Haas retrofit

    I thought that one looked pretty nice for a retrofit. Is it as nice as it looked in the pictures?

    Sorry, I don't have much good input on the servos. I did find these generic chinese 1KW AC servos with a 17bit encoder:

    https://www.ebay.com/itm/113640253066

    It has the low profile cables and based on the drawings looks like it may fit. It has the same continuous torque rating as the DC servos spec'ed above but not as much peak (3X vs 5X). I found some a bit cheaper (< $400 with drive) but they only had 2500 CPR (10000 PPR) encoders which may be on the low side if the motors are direct coupled:

    https://www.ebay.com/itm/122095801157

    I don't know the level of quality these would have and I think you'd have to assume the support would be minimal at best.

  11. #11

    Re: Servos for old Haas retrofit

    It’s in really good shape mechanically. It’s too clean to have ever done any real work. Story I got was that it had a bad spindle drive. The seller scavenged all the controls and sold them to another customer.

    I’ve found a few servos on eBay that look like they’d work but I’m a little nervous buying there.

    The guys at machmotion responded to my email confirming that fitting a proper size ac servo in this machine was going to be a *****. He recommended a 450 watt Yaskawa. I’m not sure about going that small.

    DMM has some 750 watt servos that look like they would fit. Their smaller ones have the wires in lieu of circular connectors which makes a huge difference. They replied to me and asked for dimensions so they could see if they might be able to make something work. I think the newer VF1/2’s have 850 watt motors so 750 might not be too limiting.

    I never thought I’d have any trouble with the mechanical part of this. I haven’t even got to the fun part yet.

  12. #12
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    Re: Servos for old Haas retrofit

    Dumb question - can the connectors that are on the DMM servos be removed and "flying leads" attached instead; and a different in-line connector be fitted instead? Possibly with a custom 3D-printed or machined (if you currently have a working mill) plastic cover for where the wires would exit the motor frame?

    Alternatively... can the table be cut back enough for clearance without doing too much damage to it?

    Or can an extension be fabricated to extend the motor (and thus it's connectors) out from under the table? That's what they did on my Shizouka - the motors that are on it at the moment don't fit the mountings that were machined into the table, so an adapter was made with the bolt hole pattern for the motors on one side, the table bolt pattern on the other side, and a shaft coupler in the middle. The adapter ends up adding about 5 inches to the overall length of the table + adapter + motor assembly.

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