No1Mk111 Receiver Holding Fixture

[Surpmil]

Can the accuracy and parallelism of the jigs, or the mounts be relied upon to the extent that if the locating of the machined bearing surfaces on the body is identical, the collimation of the centers of axis of the rings and the bore will be perfect when fitted up?

Maybe it is possible to achieve that level of accuracy, but only with perfect collimation of the jigs to the bore. Not an easy thing to achieve, though H&H apparently did, or close to it. But then they weren't rotating the body and they were using rifles selected for accuracy so the variables such as the squareness of the boltway, barrel threads and front face of the body could be assumed to be satisfactory. But when using unknown barrels and bodies, is it wise to assume that? Granted that Lithgow made the best SMLEs.

I can't see anything beating lasers, or a boresight in the chamber and a plain telescope in the rings for accuracy, since the collimation can be checked over 50 or feet or so against an aiming board marked to reflect the center to center distance of the rings and bore. The No.22 scope is a cheap, readily available and has a plain reticule, presumably optically centered from new, since there is no provision for internal adjustment.

Having the rings securely clamped around the body of the No.22, after the alignment of the reticule to the outside of the tube and the parallelism of the tube OD has been confirmed, might be the easiest way to ensure that when the solder on the bases cools everything is in the right place. One of those Soviet or East German boresights sometimes seen on ePay with an adaptor made to fit the chamber might be better than just a new .303 case with a hole through the primer recess.

What the built in angle of deflection was I have no idea, but no doubt you do. Tricky to get the crossbar in the front base exactly horizontal. Is there any reference except the foresight if none of the external body surfaces are reliable controls?

Probably they did most of the collimation when setting up the rear base originally? Would be handy if you could attach the front base with a single screw first to allow just a hair of rotation if required before soldering and screwing down? It's that or file out the back of the 'hook' on the front ring for whichever side is required, but no going back once that is done!

One of those odd instances where the old ways are still the best ways?

[tbonesmith]

You just gotta go with the axis of the bolt which is important in respect of fitting telescopes because you KNOW that the axis if the bolt is (? or VERY close to) the axis of the bore.

How you do it without unbreeching is....., phew!

Im thinking of doing it unbreeched, on a mandrel through the boltway, threaded into the receiver that has been machined between centres from a scrap .223 barrel. Im thinking the mandrel could be maching with 3 flats on the driving end to make it indexable in a 3 jaw chuck in the dividing head, making it removable and accurately replacable in the mill/dividing head while giving a very close visual approximation of the bore axis through the hollow mandrel. This would allow the body to be machined, removed from the mill, checked for collimation visually, replaced accurately on the mill and adjusted as necessary so you could sneak up on the collimation without having to spend forever resetting everything.

[Son]

Please excuse me if I stuff this up, I am 24 hours post op and still under the influence of some wonderful chemicals....
As far as a repeatable datum is concerned I think you need to reproduce the Wing Gauge part of the Gauge Parrallel that went into the boltway and the machined recess between the trigger guard lugs. Naturally you won't have concern yourself with the wing part as this is only needed for indexing the barrel with the gauge parallel.
At the back you can leave a bit of length on it to either incorporate your three flat sides on this part or a shaft and a centre hole, or both. You will need to come up with a set up for the front that screws into the barrel threads and then can lock into the front end of the wing gauge part through the receiver ring... Perhaps make up a collar out of a barrel stubb and bore it for a neat fitting through bolt, screwing into the end of the wing gauge.
I see this as giving you an upright datum at 90 degrees rotation from the top of the receiver on the "leg" of the wing gauge that goes to the bottom at the rear trigger guard mount. The barrel stub screws in to bottom on the inner front surface of the receiver ring, and a few thou gap from that rear face of the barrel stub to the front face of the wing gauge that can be shimmed if tightening the through bolt distorts the receiver at all.
You can also then machine three sided driving flats on the barrel stub too, but it won,t give you repeatable possitioning like the wing gauge should.
I am away from my pics at the moment, but I am sure if you aren't familiar with the shape of the wing gauge, someone can post a pic... If not I will stick one up when I get home.

Attachment 71282
Attachment 71283

With the gauge/ mandrel inserted into the receiver from the back, the alignment lug that goes into the rear trigger guard space gives you a repeatable datum from the centre line of the receiver about the boltway bore/ barrel bore. Making it extended to the front of the receiver to join up with a method of locking it in place like I suggested above to a centre hole for mounting. Leave some length at the rear to cut your three sided driving lugs concentric to the bore and mount in a 3 jaw chuck in an indexing head on the machine table.

I assume your main aim is to machine the half dovetail on the side of the receiver charger bridge for accepting the rear base mount for a HT (which has to be a very precice distance from the centre of the bore) and from that mark out the center of the receiver ring to accept the front base mount.

Because of the slight differences in the outside sizes of receivers, Looking at a HT without mounts, it is easy to work out the first machining step was to create the flat to work from. Once the flat is at the correct angle and distance from the center, then it is as simple as cutting the half dovetail and drilling from a jig the mounting screw holes.

Attachment 71285
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[muffett.2008]

Why not make up a long dead centre shaft to seat in the rear of the chamber, with a lug attached similar to Brads wing gauge to act as a turning dog and fix the location of the centre.
If you are using a long bed lathe as I do, then a live centre in the muzzle and the made up dead centre/pilot in the bolt guide will hold it on centre, then I use a Milling vice on the lathe crosslide, with whatever I need, to cut or grind.
You should be able to use your back gears as a position lock, I made up an index lock years ago to use in gear cutting which allows me to set and lock at any angle.

[Flying10uk]

My way of mounting the receiver up on a mill to perform milling/drilling operations would be to remove the barrel and make up a false stub to screw into the barrel hole in the receiver then mount this in a dividing head on the mill table. I would then make some kind of fixture to locate in the bolt hole in the receiver. I am not an armourer but I am an old school toolmaker.

[Peter Laidler]

I can sense that you're an old 60's apprentice like me Flying10. But as an Armourer, I have to say that I would be MOST reluctant to remove a barrel especially if I could machine a tapered collar that I could nip tightly onto the nocks form. Then have that collar running in a bearing. Or have that tight collar housed in the lathe chuck....... You get my drift.

But certainly, machining everything to the mechanical axis of the bore is the way to go. But be warned that in the worst case, some bodies are so worn at the rear that the bolt can seem as loose as a sausage in the high street as they say in the best circles. To the extent that the sear can interfere with the underside of the small locking lug as the bolt is reciprocated. This means the torch.........

Great thought provoking subject Tom. (From this years SD)

[Surpmil]

Since the bolt ways are not likely to be of identical diameter, perhaps a mandrel split into four for part of its length and bored and tapped slightly undersize for a bolt would allow the mandrel to be "spread" and grip the boltway behind the locking lugs, which is almost the only place it has much support.

Might be a good idea to have the same feature at the opposite end as well, though the contact area is minute by comparison. Mounted that way, the front body face could be made 100% square to the bolt way and the barrel threads at least checked.

Makes me wonder if they did some subtle barrel "truing" as part of the collimation process, ie: dropping said barrels onto wooden blocks etc.

[tbonesmith]

Thanks everyone for their contributions, it's all very helpful, and interesting and I will incorporate several of these ideas into the fixture. I'll post a drawing of what I intend to make over the next couple of days, and get the fixture itself happening this week.

All the best for Easter.

[tbonesmith]

Since the bolt ways are not likely to be of identical diameter, perhaps a mandrel split into four for part of its length and bored and tapped slightly undersize for a bolt would allow the mandrel to be "spread" and grip the boltway behind the locking lugs, which is almost the only place it has much support.)

Or maybe at the rear the mandrel could be made 20 thou undersized to allow a brass or steel bushing made to fit the individual rifle to be sleeved over? Hmmm...

[Flying10uk]

Peter, could you please confirm that the screwed barrel attachment threaded hole in the receiver is on exactly the same axis as the bore for the bolt. I assumed that it was when I made my last post and then I wondered if that was the case. Thanks.