Lapping loading taps

[bill57]

I'm looking for some advice on lapping a conical loading tap, as it's something I'm not very good at. The gun is an early Webley Osprey. I have made some attempts, but at the end the tap is very prone to binding (suggesting high spots, I would guess).

Do you guys lap the new tap from the very start, or do you size it down a bit first, such as on a drill/lathe with emery or wet and dry?

What do you use for lapping paste? I've tried valve paste, but found it very harsh, then rottenstone in oil, which seemed much better.

Do you do it all by hand, or by mechanized means?

What kind of finish do you aim for on the final surface?

All tips and advice appreciated!

[Phil Russell]

I would be very interested in the advice as well.
I must assume that the oversize tap is oversize to an extent that it does not sit such that the pellet bore is not in line with the barrel; in fact the tap sits too far out from its housing. The skill is such to get the tap seated such that everything lines up while maintaining a good air seal.
Personally I only ever 'lapped' car valves ....
So ... let's hear it from the engineers here.
Cheers, Phil

[mrgeoff]

If you lap the tap by any great amount, you will possibly start off-setting the pellet bore from the barrel bore.

[bill57]

Perhaps I should have been clearer - I'm talking about lapping in a new, oversize tap to fit. Aligning the pellet seat in the tap with the bore is part off the lapping process.

[Phil Russell]

Perhaps I should have been clearer - I'm talking about lapping in a new, oversize tap to fit. Aligning the pellet seat in the tap with the bore is part off the lapping process.

Agreed ... how is this done? I had always assumed the use of valve grinding paste and a slow approach by hand ... but this would, of course, remove material from both tap and action. Does that matter? Maybe not.

Cheers, Phil

[Vic Thompson]

Provided that the bore is sound and not scored my suggestion would be to find where the high spots are by cleaning both tap and bore carefully and then using engineers blue (or a good felt tip pen if not available) and inserting the coated tap "dry" into the bore and gently pushing home and rotating. Inspection of the tap would them show high spots as the blue would be removed by contact with the bore. You could then gently "ease" these areas with a very smooth file followed by "wet or dry" and keep repeating the process until alignment and friction improve sufficiently. The trouble with lapping in is that it's a one way process, go too far and the bore is ruined and in any case, might from then only ever work with that one particular tap. However, it might be that the bore does need a bit of finishing off and in that case It's possible that extra fine grinding paste could be used sparingly on the tap followed by chrome cleaner or brasso.

Regarding hand or machine, I'd go with hand processing and being very gentle and patient when doing so.

Just a suggestion and no responsibility accepted if it either doesn't work or undue damage occurs to either part.

Vic Thompson.

[T 20]

Perhaps I should have been clearer - I'm talking about lapping in a new, oversize tap to fit. Aligning the pellet seat in the tap with the bore is part off the lapping process.

The last one I did was well oversize so I used a fine cutting paste to lap the tap in, rotating the tap through a full rotation clockwise and then anti clockwise.

Cleaning everything off and checking frequently for alignment is a must as it's very easy to lap too far using cutting paste.

When I got near I finished off by lapping with Solvo Autosol Chrome polish, again with frequent checks for alignment --- you can check the alignment by pushing a pellet skirt first down the barrel from the muzzle back down into the tap or by simply looking through the cylinder at how the tap aligns with the bore.

I found that care must be taken when rotating a dry tap in a dry cylinder as the two can ring together as they're so closely matched.

The tap does feel a bit lumpy when dry but a smear of moly grease makes them silky smooth.


Tap lapping's a pain to get right, but when you get it right it gives an airtight seal and you fully understand why BSA changed to parallel taps.




All the best Mick

[abellringer]

At the factory they used a special reverse spiral tap on MKIII's and Osprey's, it removed tiny amounts of metal and left a highly polished tapered bore, this was done by ''experience'' using a bore size gauge to determine when the tap as almost in line; then it was lapped in with coarse paste and finally fine paste until it lined up with the bore. If you have a ''big'' oversize tap it will take a long time with just paste, but coarse first will help.