Precision machining required

[mangocrazy]

I recently took a piece of work to a local engineering firm who have done a lot of stuff for me in the past, but I was not satisfied with the result. I took it back to them and they basically said there was nothing more they could do. I don't want to fall out with them, but I do actually need the work correcting.

Basically I am trying to make a preload adjuster fit on a motorcycle shock that it wasn't designed for. I needed the internal thread machining off and the opening machining out to a fraction over 54mm. The preload adjuster has to have a clearance fit over an M54 x 1.5 thread. The problem is that the machining seems to have left a ridge part way down the sleeve, which is stopping the adjuster sliding over the shock thread.

Is there anyone local (ish) to Sheffield who has a lathe (and knows how to use it) who could machine this to a clearance fit for me? Payment in cash or alcohol is understood...

 

[doubleboost]

If you are stuck I would sort you out
Postage job though a bit far away to just call in

 

[slim_boy_fat]

and the opening machining out to a fraction over 54mm.

Define "a fraction"

 

[mangocrazy]

Define "a fraction"

When I asked the engineering firm initially to do the job, I asked for the sleeve to be machined out to between 54.05 mm and 54.1 mm. To my mind this should provide sufficient clearance for a snug sliding fit.

 

[julianf]

I'm not wanting the job, so I'm just curious -

You say you want a thread machining off and then it opened out to between .05 and .1

So, after the local place has done it, have you gone and purchased another off the shelf part that has the thread in place again?

You wanted the job between .05 and .1 - how close did your previous firm get? And how recently have had your calipers calibrated?

 

[dobbslc]

I think it's basically a large spacer that fits over the threaded part of the shock. Just loose enough to slide up and down when the lock ring is turned???

 

[julianf]

To my mind this should provide sufficient clearance for a snug sliding fit.

A thick human hair is stated as 0.15. So 3 times your lower clearence limit, assuming a perfect 54mm major diameter on the thread.

This, assuming stable temperature etc etc.

So, anything thicker than a third of a human hair over the major diameter of the thread is going to cause binding, at your lower limit. Again assuming the thread is perfect and disregarding temperature.

I don't understand your application, but this all seems pretty close to me.

 

[Brad93]

Photos speak a thousand words.

There shouldn’t be a ridge in you part. Perhaps they bored it from each end but didn’t clock the part after turning it round in the chuck.

In which case your part has been bored off centre and to rectify it will mean boring the part even larger.

 

[mangocrazy]

I accept that I may have given rather tight specifications for the machining, but the last thing I wanted was lots of slop in something that has to deal with a spring rate of 430 lbs/in. On looking closer at the machining, there are ridges easily felt by a finger (not even a nail) at about one-third depth in the sleeve, at 3 points around the inner circumference. Hopefully the photos will show what I mean.

This is the shock minus spring with preload adjuster off.

This is the adjuster on the shock as far as it goes without binding.

And this is the machined surface showing one of the ridges. There are 2 more like this, fairly evenly spaced aound the circumference at the same depth, easily felt by a finger tip.

 

[PhillipM]

Have you got any photos? What size is the current piece they've done?

Edit, never mind, I can see them now, perhaps clamp marks from wherever they held them down, I'd go for more clearance, all my sliding damper sleeves are at least 0.5mm oversize, the shock will expand with heat and bind it if you make it too close as well.

 

[mangocrazy]

Yes, definitely needs more clearance (Clarence), but those ridges are at least half the problem.

 

[rory1]

It’s a bit of an odd job to chuck. If I were to do it I’d put in on the mill and use a boring head

 

[PhillipM]

Yeah, I would have offered but I can't chuck that up. You could probably clean it up some with a 3-legged hone if it's a ridge.

 

[Brad93]

That needs to be done in a mill.

 

[Brad93]

That’s a job for @doubleboost

 

[mangocrazy]

Well, he has offered, so... With the current weather that could be a nice ride out on the bike (not the one with the shock missing, obvs...)

 

[erasma]

CNC milling machine could do that

 

[Hopefuldave]

Looks like a 3-square bearing scraper would do it...

Dave H. (the other one)

 

[gordon stephenson]

If its only got to be close fitting to slide over the treaded portion, A decent scraper would sort it out in no time,

 

[brightspark]

a flap disc in a die grinder and use micrometer blue. it doesn't have to be that accurate