A question for precision machinists

zoidberg

zoidberg

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I'm having 'bits' made up for a steering-linkage modification, involving a Universal Joint and an extension-piece turned down to fit into the U-J, and both drilled through for an 8mm nominal bolt.

51107125688_89b4147425_z.jpg


The extension-piece takes the bolt through with little 'slop', but is slightly oval.

51106653647_0d0208c926_z.jpg


The U'J also take the bolt through with little 'slop', but I am unable to pass this '7.7mm machine screw' through when both components are lined up.
It appears the holes drilled through the U-J are not diametrically aligned.

51106970684_36ef708e40_z.jpg



What's the optimum way to fix this, to avoid 'lost motion' in the steering assembly?


:rolleyes:
 
It depends on your facilities, are you able to clamp them accurately and drill them yourself?
If you want to continue using that method, why not drill through both simultaneously with an 8mm drill bit.

Will you need to dismantle them in future? If not, weld them.
 
How much misalignment? Who drilled the holes? Can you measure to see which is incorrectly drilled? Can you get another part made?

How much torque is transferred through the joint? Do you later need to be able to disassemble?

Easiest, assuming strength of joint isn’t an issue, is to use a smaller bolt. Maybe a higher grade.

The “precision machinist” would throw the incorrect part in the bin and make another ?
 
Poignard said:
Use a reamer
Click to expand...


I think that it is possible you could get somewhere by using a tapered reamer and then fitting a taper pin. Unfortunately your pictures don t really help and it looks like not only are the holes in the UJ out of line but going by the pictures the hole in the extension is also off centre. If this work was done by a reputable machine shop then take it back. If a cowboy then the tapered pin solution. However depending on the misalignment you might also be better of also drilling another hole through the extension in the right place at 90 degrees to the off centre hole . A machine shop should have the tools to do this.
 
I'd use a 7.6 or 7.5.. mm drill bit to see how far out it is.

A precision machinsit might not use a threaded part of a screw to locate the two parts.

Personally, I would ask myself whether running an M8 tap through it would do the job. Then pin it with two grubscrews perhaps. M8 in 7.7mm is a bit skimpy, but how much material is there to play with? A bigger thread migh weaken things?

Real engineers understand how accurate things actually need to be and reliably make things at least that good.
It might not be what you hoped for, but is it within tolerances of the drawing?
 
Bilgediver said:
I think that it is possible you could get somewhere by using a tapered reamer and then fitting a taper pin. Unfortunately your pictures don t really help and it looks like not only are the holes in the UJ out of line but going by the pictures the hole in the extension is also off centre. If this work was done by a reputable machine shop then take it back. If a cowboy then the tapered pin solution. However depending on the misalignment you might also be better of also drilling another hole through the extension in the right place at 90 degrees to the off centre hole . A machine shop should have the tools to do this.
Click to expand...
What he said.
 
Could you not drill another hole at 90 deg to the original through two parts assembled pilot drill first. Is it possible that the hole can be opened up to 10mm. Without seeing more of this restricts ideas to solve the problem.
 
In my considerable experience reaming SS is not to be undertaken lightly. If the reamer ever skids it work hardens the surface which quickly blunts the reamer. Tricky to keep a reamer, especially an adjustable one, from skidding when using on SS. Also, without a guide or jig, to keep it straight.

I would drill through while assembled and select a tight fitting - or make one - bolt to hold it together.

The shank diameter of the bolt, not is nominal size, is the size to be aimed for. The threaded part should be clear, or almost clear, of the bored hole. The shank should fill the bore and be tight on both pieces.

Two different makers can use two different shank sizes. They might only vary by a very tiny fraction, but they do vary.
 
Thanks to all for insight.
I won't try to tackle this myself, but I'll take it back.

Here's the general arrangement that's wanted:

51108328060_454a2945ed_z.jpg


The object is to lift the rudder post/tiller connection up, through the stern deck, so that the tiller can be raised up out of the way when so wanted.
The original way brought the tiller inconveniently out through a slot in the cockpit rear wall.
 
Bilgediver said:
I think that it is possible you could get somewhere by using a tapered reamer and then fitting a taper pin. Unfortunately your pictures don t really help and it looks like not only are the holes in the UJ out of line but going by the pictures the hole in the extension is also off centre. If this work was done by a reputable machine shop then take it back. If a cowboy then the tapered pin solution. However depending on the misalignment you might also be better of also drilling another hole through the extension in the right place at 90 degrees to the off centre hole . A machine shop should have the tools to do this.
Click to expand...
A taper pin would be good after reaming with a taper reamer. Or ream parallel and fit a roll pin.
 
Is this an emergency tiller arrangement or the real deal? What is acceptable for the latter may not be for the former, personal foibles not withstanding.
 
Yes, Penfold, I agree with that. The intention is for this to be 'the real deal' - and I want it to be robust.

I shall have the option of the 'reversionary' setup - should it become necessary, and I'm also musing on a completelyindpendent steering arrangement.
 
The paisley pyjamas answer is a matching pair of keyways in shaft and socket with a grubscrew to pinch the key into the shaft; shaft ought to be a snug sliding fit in the socket. I'd be happy with Bilgediver's taperpin and(again assuming a snug sliding fit) the shaft and socket well smeared with high strength stud locking compound. Belt-and-braces luddites might prefer having the two seam welded together, but this would introduce a heat-affected zone and stainless likes cracking enough as it is.

Because of the universal joint arrangement the bearing where it comes out of the coaming will take some odd loads and the rudder post extension is quite a cantilever; is there a special reason the UJ cannot be fitted/attached directly to the rudder post?
 
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