L42 Style Build

[CINDERS]

Looks like things are going well for you with the build it shall be very nice when its finished no doubt also is that a No. 32 scope that PL has refurbished for the project.
Will look forward to seeing the results on the range.

Information

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[tbonesmith]

Hi Guys,

Today I drilled and tapped the rear pad in situ. I still don't have the 1/4 BSF tap for the rear hole so that will have to wait.

I managed to break a tap in the front screw hole on the rear pad, I think I accidentally picked up the intermediate tap. Anyway I punched it out and tapped it with the right tap and there was no harm done. Beyond that I fitted and modified the rear sight.

I'm stuck until I get that tap now. Hopefully this week, then I can get everything stripped, bead blasted and blued pretty fast I hope. In there mean time I suppose I can the timber work happening.

[tbonesmith]

Hi Guys,

I'm giving the steamed warped timber a run. So I milled out the barrel channel and have half lapped the rear guard through the radius to extend it forward of the mid band. I've done this a few times and it works well. Where I have drilled out the rivets I will plugs these holes with beech or birch plugs. Again this is a modification illustrated in another of Peter Laidlers great articles: Milsurps Knowledge Library - The fore-end and handguards of the L42 (by Peter Laidler)

I have also inletted for the larger knox form.

The last photos show small pieces glued back into the barrel channel, when I milled it out I think I went a little too far and was worried that the forend might be a bit delicate or crush under the top wood. So I machined square recesses and glued in some bits to reinforce the area... I'll measure better next time.

So hopefully I can get the rear guard sorted out tomorrow.

I have a decent SMLE (No1Mk3) butt to use for this build. I'd love to use "all correct" parts, but this butt will fit up fine and I don't really want to go chasing parts for a no collector value job like this. Perfectly functional will be just fine thanks, and the wood will refinish really nicely.

[xa-coupe]

What are you going to do for a cheek piece? I see them advertised but at circa $70 I haven't been in a rush to buy one.

[tbonesmith]

Well the tap my mate sent me turned up today, so I drilled the body for the rear bracket screw (1/4 BSF), it was very hard not surprisingly and I promptly broke the tap in the hole. So that was good. I managed to punch it out by shattering the tap, then I ground the stub of the tap and had another go and broke that too!! Perfect, so I smashed that out as well. The hole has a tiny amount of damage to one of the threads, but nothing that won't clean up. Sorry Gary, I will give you new one!

I have a new set on their way and I expect them next week, hopefully I'll get through with a brand new taper tap. I expect if I can drill it with HSS I should be able to tap it with HSS. If anyone has advice I'm all ears.

And with regards to the cheekpiece, I think I'll make one from scratch.

[flying pig]

Tbone, what are you using for oil? A friend of mine that is a master fabricator told me to use Rapidtap brand cutting oil on my Long Branch build last spring. That stuff glides amazingly. The tap gets tight but there is no stop start to its movement, just smooth spin. I only broke one 4Ba tap and it was because I got greedy and tried going too fast, I knew better as I had a lot of torque on that tap

[tbonesmith]

I was just using a general purpose grease-like metal cutting compound.
This stuff: 40004 Molyslip Metal Cutting Compound

I have had and used the stuff for ages, seems good usually.

[CINDERS]

Would different metals present different gauling resistance as I am not a machinist just a question on the tap Tbone?

[tbonesmith]

I don't know. The main thing is that where this hole is located is right next to that recess for the locking lug and the metal there is extremely hard. I think I'll get there with the new tap, but I'll let you know if I don't too.

[ArtioZen]

Hi T-bone - thanks for the great project write up - better than any mini-series on TV!

Rapid-tap and other lubes are good - tend to be "thin" and function against galling - good for soft alloy steels etc - I have used it extensively and other expensive tapping only potions with unecessary lube / pressure additives..

The best I have ever used was old school "sheep tallow" - also by other glamorous names (smells like victory)- stayed put in the hole and tap, eased pressure at the cutting edge and had "body" to move chips out of the cut zone (watch out for that with thin lubes).

I assume you are tapping in the machine head (driving by hand) for position, axies and feed control - you are obviously a serious machinist so I doff cap if any of this is a given and is already your practice / experience (it may benefit others etc):

Good quality HSS should be good to go on carbon steel (many holes as life expectation and a $ sting reassures quality) - the locking lugs are reported to be a thin case hard so taps should eat the soft center - the crunchy outside is tiny compared to the thread pitch (all taps need to chew, chew, chew - 1/16 of a turn forward, 1/8th back)...and should be light and easy like the drill...blinding and raising the hole by taping / waxing the inside wall (or other dam method) can provide a better lube reservoir if its the runny kind.

Most of the broken tap frustration can be dealt with in the hole - the drill should cut and produce low pressure, dwell (heat in the hole) and a smooth bore and be of the "right size" - check the tap root diameter to the hole size of the drill..I was taught that a 75% form thread is almost as strong as a full form thread, and in this application the thread is only required to produce a light axial load - reducing tap load increases its life.

Often the end from of the fastener thread may also benefit from extra clearance - which can also increase the lead on a hole for a tap to start - think chamfer - I would be temped to touch the pad chamfers when prepping these holes myself...

The drill should not exhibit "wobble or wonder" - this is typically shared by the tap and is a known killer - fix that in the hole with the drill or a mill etc. Reaming the hole to size and finish is an option (not talked about much these days...).

A taper (lead) tap should have 8-10 full thread turns between clearance and full form teeth - manufacturers / suppliers tend to shrink / skimp / offer an intermediate tap (@4 turns) for a "taper tap", smaller taps are best with a single flute for strength.

The tap drive should be "hard" - no slop or backlash - use a tap collet if poss, (the tap itself possessing great quality location / drive features) the axial feed should provide no wander or end pressure (up or down) beyond the pull of the thread pitch when the tap bites.

Similarly all of these factors are in play when hand tapping also - that's where mastery comes in!

I have some taps that are 40 plus years old - sorry, nobody can ever "borrow" them - they represent my livelihood and I don't run em like I rented or stole em!

I hope this helps, and I look forward to another gripping installment!