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I have a question about the plastic part that joins the two metal parts.? The plastic part has 2 cylindrical cutouts that are 90 degrees apart.? The mating metal coupler parts slide into these two cutouts.? One of the plastic cylindrical cutouts looks like its worn-out and the mating metal cylindrical part has play along the coupler axis and can be pulled out.? Should this motor-to-worm coupler be replaced?? Can I just buy the plastic part?

It’s the DEC coupler and I think this may be causing some of my SLW backlash.

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Jim W
Phoenix, AZ. USA

Losmandy GM811G

It’s an Oldham coupling. ?Usually you replace the lot as grub screws can be worn etc. I believe Losmandy had 2 lengths of these depending on the worm block but not so sure on this. ?

You can use a “Ruland bellows type” ?coupling but many users have said the Oldham performs well or no noticeable improvement in changing to such. ?

Ensure alignment of shafts I’d good during replacement ?

cheers


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Brendan

Hi Jim.? Though I don't think this will have much affect on your backlash issues (it didn't for me when I tried), if you want to try, the company who makes the coupling will sell you the nylon centrepiece if you ask (in 2018 they quoted me $4 each + shipping).



Ruland couplings are quite expensive and I think the cost/benefit might be high (and perhaps why Losmandy still sells the original OPW, but without the Ruland coupling).

Keith

Here's my concern.? The nylon center piece is worn enough where the mating metal coupler can move along the axis and almost pull out on one side.? With the SLW's the 2 cap-screws holding the?worm bearing blocks are not tightened down and can move.? Without a fixed point holding the assembly tight the assemble can shift wide to side and cause backlash..

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Jim W
Phoenix, AZ. USA

Losmandy GM811G

Jim,

I hate the grub screw Oldham coupling they are an abomination. Those grub screws distroy your worm if you ever want to replace the bearings. You end up filing the thing which will ensure a larger 240s error, because they never fit square to the shaft again. I went over to Rutland JC10-4A, JC10-3A, and JC10/15-85B. Metric sizes are also available should you want to change your gearbox. They clamp around the shaft, not dig into it. I'm still looking for other clamp style fitting that will allow some differential slip but have not found any. There ?is very little available for a 5/8" outside diameter, unless someone knows of anything? There is a procedure I have to ensure the motor shaft is square to the coupling which I can explain if anyone interest?

Peter

Which one do you recommend?

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Jim W
Phoenix, AZ. USA

Jim,

Those part numbers define on complete coupler for 1/4" on one end and 3/16th on the other. You need all three pieces. Let me get my order in first though just in case they are in short supply?

Peter

OK

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Jim W
Phoenix, AZ. USA

Jim, In case it wasn't clear, an Oldham coupler is *supposed* to slip along those groves yet not have play when the shaft is twisted. The purpose of an Oldham is to allow connection of two shaft that are not perfectly aligned along their axes of rotation.?
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Edward

Hi Edward.? Yes, I understand.? My issue is that one side can be pulled out along the axis of the coupler while the other side is tight with no play.

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Jim W
Phoenix, AZ. USA

Losmandy GM811G