Lap for a bronze bore.

I have two 13mm bores to lap and they are made of bronze, any tips on the lap materiel and grades of compound to use.

I have 600 and 1000 grade compound that I can use.

I need to remove as little as possible.

Clive

Lap has to be softer than the material to be cut and allow the abrasive to embed, so I'd suggest an aluminium alloy or even wood.

Neil

Thanks for the reply Neil, my thoughts also and was considering making a lead lap.

The job at the moment has to be mounted on a mandrel to machine the outside and I was considering using that as a lap but it is steel.

So I think I will go with the Alu. lap.

Clive

Hi Clive, If you need the lap adjustable make a lead lap, I have made many of these to lap barrels. I knurl a BMS rod then drill and taper ream for a taper pin, split this section of the BMS rod and deburr the inside for the taper pin then cast an oversize section of lead over the knurled section. I made a split alluminium mould for this.

lastly turn to the diameter requiered and "load" with lapping paste by rolling the lap on a glass plate. It can of course be expanded by tapping in the taper pin. Oh and don't forget to put some oil in the bore and wash well when fininshed. For an extra fine finish use pumis mixed with oil but I have not used this on bronze.

Good luck John.

hi clive,

i would split a length of 12mm copper tube inserted over a wooden dowel and use that as a lap, or else use a wooden dowel with very fine wet and dry paper (1200 grade) wrapped around till reasonably tight in the bore. wash out afterwards with paraffin. it is very important that the lapping compound cant be squeezed into a recess and cut deeper than required.. hence a split lap or the use of fine wet and dry paper (in it's dry state), plus the use with (very fine) compound of a lap that must be softer than the cylinder material. avoid valve grinding paste like the plague... it's far too course for our requirements. if you use 'brasso' make sure it doesnt dry out during the lapping process. personally i prefer 1200 grade wet and dry paper.

good luck!

cheers,

julian

I use wooden laps, turned to a sliding fit, and split down the middle, a wood screw is fitted in the slot to expand the lap as required. Ian S C

can someone please explain this process to me...i thought it was akin to honing but now im confused???

OK, I have carried out the lapping of the bores and I used a piece of PTFE rod.

After turning it to a push fit in the bores I slit it down the middle and then put a screw in the end and used 1000 grade abrasive.

Its come out fine with a matt finish on the surface in the bore, more than good enough for me.

Clive