Author Topic: Fork spindle thread  (Read 413 times)

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Offline saluki42

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Fork spindle thread
« on: 13 Jun 2022 at 11:11 »
Hi can anybody tell me the fork spindle top thread details for a 1934 Model Z. The spindle measures 1 1/6" diameter with what looks like a 20tpi thread so I just turned up a couple of nuts using a 1 1/16 BSCY course tap but no way will these nuts fit the spindle.

So my question is have I got that thread right?

Offline eddie

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Re: Fork spindle thread
« Reply #1 on: 13 Jun 2022 at 11:49 »
When you say the fork spindle, I presume you mean the steering stem that goes through the steering head bearings. Having obtained a tap, make sure it is exactly the same diameter as the steering stem. If that is the case, offer the tap up to the side of the stem to make sure the thread pitch is also identical. If the diameter and the pitch both match, I would guess that there is some damage to the top of the stem - either from the stem being drifted out of the bearings, or something being inserted into the stem and swelling it. This sort of damage is usually limited to the first 2 or 3 threads, and careful easing with a thread file usually remedies the situation.

  Regards,
                Eddie.

Offline cardan

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Re: Fork spindle thread
« Reply #2 on: 13 Jun 2022 at 11:49 »
Hi Chris,
There seems to be a typo in your post (1 1/6 vs 1 1/16). Are you talking about the steering stem rather than a fork spindle? 1 1/16" (1.0625") diameter?
1 1/16" is a funny size for a stem (but that's nothing for Douglas!), and 20 tpi is rather coarse (ditto). Lay your tap alongside the thread (as if it were a thread gauge) and see if they line up.
(BSCycle standards for steering stems are 31/32"-30tpi, 1"-24tpi and 1 1/8"-26tpi, but as we know Douglas were not followers of standards.)
Leon

Edit: Sorry, seems that Eddie and I were typing at the same time, luckily with the same ideas!

Offline saluki42

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Re: Fork spindle thread
« Reply #3 on: 13 Jun 2022 at 13:26 »
Thanks for the quick response to my question and yes I did mean fork stem. The problems I have at present are I don't have a 60 degree TPI gauge only the Whit. 55 degree version and the metric equivalent would be 1.27  pitch so no easy gauge size there also I have a first taper tap of the 1-1/16 x 20tpi so the lead in is as long as the stem thread itself so getting a decent gauge length there is tricky. This is why I was trying to get confirmation of the stem thread size so at least I had one thing to work with.
Oh and the stem 1.0575" diameter reducing to 1.0523" for the thread

Chris

Offline EW-Ron

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Re: Fork spindle thread
« Reply #4 on: 13 Jun 2022 at 21:38 »
The problems I have at present are I don't have a 60 degree TPI gauge only the Whit. 55 degree version

Does anyone have anything other than the Whitworth version ??

Offline eddie

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Re: Fork spindle thread
« Reply #5 on: 14 Jun 2022 at 07:20 »
It doesn't matter which version - they are a thread pitch gauge, not a thread form gauge.

   Eddie.

Offline saluki42

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Re: Fork spindle thread
« Reply #6 on: 25 Jun 2022 at 09:16 »
Hi all thanks again for the help and problem now solved. The supplier of the 1-1/16" x 20tpi tap sent the wrong one and what I got was a UNS tap, same diameter, same thread angle and correct tpi but the root and crest radii were wrong. He's now sent, free of charge, the correct Bscy tap and the nuts fit perfectly.

Chris