Best way to finish a 10mm bore

[creep_pea]

Hi

I'm making a 1 off brake master cylinder in aluminium, it has a 10mm bore by 45 deep for the piston with rubber seals to run in, obvisously the bore needs to be a good size and finish.

Any recommendations for cutting it to finished size?
Never had any luck using standard reamers, like sheaf cut reamers but never tried them in ali, could bore it but dont think I'll achive the required finish.

Thanks

Chris

[HuFlungDung]

Ream with plenty of WD40. It should come out pretty nice if the reamer is new, sharp and well aligned with the hole.

If I was being fussy, I would drill it, then bore it, leaving .005" to ream. Take care with the reamer, to clear the chips before you go for the bottom of the hole, if it is a closed ended cylinder.

I might also attempt to polish it a wee bit with crocus cloth (rouge). Use maybe a 1/4" dowel, hacksaw a lengthwise slit down the end for about an inch. You then insert one end of a strip of the cloth through the slit, and then wrap it a couple of times around the dowel, with the abrasive side out. Keep it wrapped with fingertip pressure, until you get it into the hole. Then, you can polish as you see fit.

[creep_pea]

Yeah might just give that a try, I've used paraffin a few times on aluminium jobs it definitely helps with the finish, does WD40 work better?

Still not right keen on using a reamer, the number of times they have cut big on me!

Although they usually are old and probably knackered so I'll get a new one and see how its goes

Thanks

Chris

[MrWild]

Get some "A-9" aluminum cutting fluid. Green can, green fluid, much better than parrifin, kerosene, lard, or WD-40. Nice nice finishes. Because the material is soft, I'd discomend any honing. Grit particles become embedded in the material and cause premature wear in the componants that slide through the bore.

[Tinmuk]

I would reccomend boring it to size. You have much better control over finish diameter and surface finish. Rember, in a brake cylinder diameter is not as important as surface finish. The rubber cups seal the fluid, the piston just gives it strength and keeps the cups lined up with the bore.

If you make bore first, then you can make the piston a nice fit in the bore.

In my shop, we routinely bore to +/-.0001, We rarely resort to honing or reaming, mostly to rework undersize holes that can't be rechucked.

[Geof]

I read an article about "ball sizing" which wasn't sizing balls it was using them to finish holes to size, in particular holes in soft materials. You bore a few thou undersize then force a highly polished steel or carbide ball through the hole. This smears all the high spots down and gives an accurate size and a polished finish. With a blind hole it might be tricky getting the ball out so just make your master cylinder 10mm longer and leave it in there.

[ViperTX]

Well firstly....you have to determine what the proper finish is......what bore finish do you need for the seal.....

[creep_pea]

Hi

Thanks again for the most helpfull replys

Will have a look for some "A-9" aluminum cutting fluid but I've just had a quick shearch on google and it dosen't look like its availible in the U.K., might find somthing similar though.

If boring it what do you recommed, feeding in and out or feed in stop spindle and movetip away from the job before rapiding out, also what kind of boring bar do you recommend and HHS or Carbie tipped.

Ball sizing sounds interesting, never heared of this method before but might try it on a bit of scrap and see how it goes, I presume you must use some kind of lubrication.

As for the finish required, to be honest I don't know but I'm guessing at least 0.8micro m (32micro.inch) if not better.

Cheers

Chris

[DareBee]

A couple of things.
Similar to the ball thing I have burnished soft material before. Part was bored .002-.005 small and then a burnishing tool was run in, it just mushes the material out makin a mirror type finish.
The burnishing tool looked like a reamer with rollers instead of cutting flutes. I have no idea where to get these tools, I did this WAY back in my apprentice days.
Another note about reaming, I have had very good luck with taking a hone stone and dulling the cutting edges of a reamer to keep them from cutting oversize as well as greatly improving surface finish, basically this makes the edge negative rake instead of positive rake.

[Geof]

Darebee's post prompted a, maybe crazy, idea; take an old and dull reamer and run it backwards to act as a burnishing tool. Lots of lubricant, could be worth a try???

[HuFlungDung]

Darebee's post prompted a, maybe crazy, idea; take an old and dull reamer and run it backwards to act as a burnishing tool. Lots of lubricant, could be worth a try???

OMG, cover your eyes! Geof has suggested the unpardonable sin! Iieeeeyeee!

[Geof]

Hu;

That almost equals the responses I garnered when I said I was going to drill and tap holes in the table of my VMC. The difference is, I suspect, you may not be, absolutely, completely serious; the other responses were.

But I went ahead and drilled and tapped anyway.