Bore hone

[Martin DowingParticipant @martindowing58466]

[Martin DowingParticipant @martindowing58466]

I am refurbishing badly worn and abused rotary vacuum pump.

After correcting bore on the lathe I have honed it with 3 stones @ spring engine cylinder hone which you can get from car store.

Machining marks are removed but I want a better surface finish. Now it is grayish and it should be shiny.

I cannot get finer grit stones to get there but I have several grits of diamond powder (Chinese are giving it now away for free).

I would like to make a good hone out of this diamond dust.

My idea is to make repacement "stones" for my car hone using anneled copper strips with fine diamond grit pressed in on a hard plate.

Alternative would be to mix a bit of diamond dust with epoxy or UV hardening methacrylic glue and apply it on the surface of 3 copper strips to be used as replacement stones.

It is important for diamonds to stay on my lap and not get embedded during work into my cast iron pump bore – what would be disastrous for the pump.

Are my ideas correct or there are other ways to make these honing stones?

[JasonBModerator @jasonb]

Probably better to think of lapping with the powder mixed with oil to make a paste, a lap will also give a rounder bore.

I'd go with silicon carbide powders or you could use "Timesaver" which is said not to embed

Ramon's thread on laps is a good starting point

Edited By JasonB on 25/10/2020 07:44:45

[Clive HartlandParticipant @clivehartland94829]

Looking at a recent commercial machined and honed bore I notice that the honing is spiral in both directions. In fact a polished boe is not desirable as bedding in of the piston and rings needs some slight surface roughness.

My Son was a, 'Blue water Engineer' and on overhaul of ship engines they used a hone that consisted of abrasive balls on wire stalk with a hand held electric drill to rough the bores before re-fitting new rings on the pistons. These engines (Doxford) run for many hundreds of hours at constant speed

I have re-built my own car engine a couple of times over the years and used commercial vendors to do re-bores

and the bores were nver polished.

[not done it yetParticipant @notdoneityet]

Is this a rotary or reciprocating pump?

[John PParticipant @johnp77052]

Hi

Published in MEW 207 was this cylinder honing tool, mostly
made from scrap materials has formed aluminium shoes
that have suitable grades of abrasive glued on, or lead
strips which allow for embedded abrasive.
It fits around 2 1/2 to about 5 inch bores.

Don't know if that you should leave a cross hatch pattern
on a rotary pump bore i imagine that it would be an advantage
to allow the vanes to run in ,in any event using lead strips
would allow a variety of abrasives to be used.

John

[Martin DowingParticipant @martindowing58466]

@not done it yet,

It is rotary pump with eccentric spindle. Some grit went into a bore during work and it was scored badly. Performance was so bad (~1 Torr v. original 0.005) that former owner gave me this pump for free. So bore was corrected and spindle of slightly higher diameter is to be remanufactured (quite a fun to make such a spindle with a slot btw, but getting there).

So there is no reciprocally moving piston in this pump, only a spring loaded slider.

@Clive,

Have seen new bore of such pump. It is not mirror polished but still shiny and one I made, even if of rather high quality now, is still grey. In new pump bore is seen as glazed and my is not yet there.

@Jason B,

2-1/4 inch bore, so lap would be rather "industrial". Can be made for sure, but is it worth for an odd job?

There is not even a piston, only a slider moving in this pump.

 

@John,

I am exactly contemplating something like that. To save myself work I would make only shoes to install on cheap commercial hone.

I think about epoxy or methacrylic  bound diamond, though I have also some other ideas like mixing diamond powder with soldering paste and fusing it on edge of copper shoe, then pressing it hard against carbide plate to make edge straight or (if we want a long lasting hone) then I could attempt to compress diamond powder mixed with silver or indium powder (yes, have both) to make some sort of composite, which then could be soldered to the edge of hone – such product should last practically for ever.

Edited By Martin Dowing on 25/10/2020 09:49:50

[John PParticipant @johnp77052]

Hi

Found a slightly better photo of the parts of this hone, seen here
the forming block and die on the right and on the left some
pressed aluminium shoes.
Using the die the abrasive strips are glued to the shoes
and pressed on a rubber strip until set.

John

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