[JohnH]

Let’s see how many I confuse and how many agree.

If the original internals (1919 of course) are designed to have proper clearance with 3/16” (.1875”) side plate on each side and you replace the right hand side with a theoretical ¼” (.250”) thick side plate the difference in thickness between side plates is only .0625”. Shouldn’t that be all that is required to mill off barrel extension, lock frame, and bolt?
Most instruction I have seen and been given call for milling .070”. So in effect I am increasing the original clearances allowed by another .0075”.

Now the above numbers are if your side plate is a true ¼” (.250”) thick. I measure mine and it started life at only .240” thick and then milled to a true 3/16” (.1875”). This makes my ‘step’ on side plate only .0525”. If I now mill the .070” as specified I will be increasing the original clearance by another .0175”.

 

[TbcSEOD]

I see what your asking but I don't think the extra .01 is that big a deal really - unless your building an accuracy rifle.......

Also the internals are not actually riding against the simi island either, they ride against the side plate itself at the top and bottom.

Lastly (as you already pointed out - not all plates are true, so if your going by "general practice" measurements there has to be a little wiggle room.

Just my view on them.
~T

 

[tomt]

.070

tell you what i do. the .07 is fine on everything -except the lock frame !! i fit it to the reciever. that way the little ear that pushes the bolt lock down will be as thick as possible. that is the part that will break !!!! so i fit it to make it as durable as possible. HTH. thanks. tomt

 

[30calmachinegunner]

all the broken lock frames I've seen had the ear on the unmilled side broken

 

[TARGSHOOT]

speaking of broken lock frames, the only ones ive seen break were the cast type, anybody notice this too????

 

[JohnH]

Thanks Tom!!

I'm so glad we saved that piece for last!
I'm really lucky I have a perfectionist machinist for a friend and we are both building a 1919. He does really tight tolerance work for aerospace and high tech industries using Haas machining centers. For our internals we are just using one of the several Bridgeports in his shop. Even with that you can see in the last pics the kind of tolerances are parts will be machined within!
Thanks again Tom.

 

[Mouse]

I'm so glad we saved that piece for last!
I'm really lucky I have a perfectionist machinist for a friend and we are both building a 1919. He does really tight tolerance work for aerospace and high tech industires using Haas machining centers. For our internals we are just using one of the several Bridgeports in his shop. Even with that you can see in the last pics the kind of tolerances are parts will be machined within!
Thanks again Tom.

Shop?
That ain't no machine shop it's to clean!

 

[Lucky#13]

Well, I certainly have no problem with tightening the tolerances. I would add however, in addition to the lock frame being a factor as tomt points out, the internals are guided largely buy the lower rails on the barrel extension at the breech lock cam, and the upper rails that the bolt rides in. The side plates have little to do with it, short of locating the lock frame, the cams and securing the charging handle so it doesn't fly out. JMO.