McLennan Gearboxes for G11 - a problem

[adman]

I am upgrading an older G11 to gemini, which entails new McLennan gearboxes and I have splashed out on two one-piece worm blocks as well.

The problem I am having is that the output shaft from the McLennan gearbox (http://uk.rs-online.com/web/search/searchBrowseAction.html?method=sear chProducts&searchTerm=336-444&x=0&y=0) is smaller than the bore of the Ruland coupler (http://www.ruland.com/ps_couplings_disc_dsd.asp) that connects it to the worm. Can someone please tell me what the diameter of the standard Losmandy gearbox output shaft is? Does anyone know of a way around this other than to have an adapter custom made?

Cheers
Adam

[wasyoungonce]

Adam..try small parts (http://www.smallparts.com.au/store/categories/coupling/) for a bellows coupling. They are not cheap but they do have some cheaper versions. Sometimes they come in different in/out shaft sizes (like this one (http://www.smallparts.com.au/store/partslist/couplingsbellowssetscrewbrass/couplings/wide/1/))..some times they are both the same. That said they all appear metric and the Losmandy will definitely be imperial and the McLennan is metric.

If you buy one that has a some in/out bore....then bore the other side for the larger shaft.

Can be done in a drill press...maybe make a holder for bellows so it is kept perpendicular.

Sorry i don't know the Losmandy dimensions. FWIW.

[adman]

thanks for the links - some very interesting stuff on there.

I'm not sure whether it would be possible - but I was thinking more along the lines of a sleeve for the gearbox shaft with an outer diameter suitable for the Ruland coupler. So you would slide the sleeve over the gearbox shaft - maybe secured with a recessed grub screw - then slide the whole thing into the coupler?? But where the hell do you get one of those?

Adam

[wasyoungonce]

Well I did think of a sleeve..would be kinda of thin..but small parts do sell phosphor bronze bushes that can be bored & or reamed to size.

You might have to also late cut the sleeve outer diameter. Maybe a sleeve that presses on to the McLennan output shaft?

A lot of bother.

[JohnG]

Don't know if you have this site at all, shows steps relating to the McLennan Gearbox, I do know there was some discussion on that topic on the Losmandy User Group some time ago, I am not a member anymore so I can't direct you to the specific posts, a search of the Data Base may bring something up.

http://www.wilmslowastro.com/tips/mclennan_gbox.html

Cheers

[adman]

yes I'm starting to think its going to be easier to go back to the standard (albeit plastic) losmandy gearboxes....

Another thought I just had would be to get some more couplers made straight from Ruland. I am pretty sure they have metric and imperial bores - just not sure whether they can do both on the one piece...?

[adman]

Thanks John - I had seen that one recently, and its a very handy reference, but I think he was still using the Oldham coupler, so wouldn't have come across this problem - I will do a search of those forums though.

Cheers
Adam

[Hagar]

I just happen to have a new Losmandy gear box sitting here.
The vernier callipers tell me the output shaft is 4.75mm, 0.186 inch.

[adman]

Thanks Doug,

that makes sense The measurement of the Ruland coupler bore is 0.1875" (4.7625 mm).

cheers
Adam

[adman]

well - this one has led me on a merry chase.

It looks like I can get another variety of Oldham coupler that will do the job. The trick is to buy two couplers - one 4mm metric bore and one 1/4" imperial bore, them mix and match the two ends. They come in either set-screw or allen-screw clamp.

Can somebody more engineering-ly oriented than me give the coupler specs the once over and make sure that the alternate coupler is suitable?

Here are the links:

1. The Ruland coupler that was supplied with the one-piece worm. Its part number is DCD10-3-4-A (http://www.ruland.com/ps_couplings_disc_dcd.asp)

2. The alternate Oldham coupler. They come in a variety of diameters and lengths that will be suitable. (http://www.hobbyparts.com.au/store/item/cpol15260400as/couplingsoldhamcomplete/)

From an installation point of view I would probably prefer the set-screw ones - is there any advantage to either the clamp or set screw that I need to know about?

Thanks,
Adam

[wasyoungonce]

Well...FWIW..I thought the Ruland couplings were mainly for high rotational speeds..aka to dampen vibrations coupling a pump to a motor..etc.

I noticed the new Losmandy adjustable worms have a Ruland type coupling...so they must be ok to use.

The oldham....I cannot really say apart that they used them for years, although many users had complaints about them.

But...that said.....these versions are vastly different to the old Losmandy types,so yeah...these coupling look ok.

I think the clamp might be better as it shrinks down the collar to fit the shaft...where are a set screw clamp clamps on to the shaft and could give more misalignment between both collar and shaft.:shrug:

[adman]

yeah - apparently those rulands can handle up to 10,000 RPM.

I have to do some measurements of the one-piece worm block to see how much space there is in there for a coupling. There are a few different sizes so I am pretty sure one will fit.

Adam