Measuring 1911 trigger slot

Froneck · Jan 4, 2022

I have just about every kind of measuring instrument from Starrett and a few by others that Starrett don't make. I'm looking for an accurate way to measure the slot for the trigger, not the bow the trigger attached to the bow's location. Anyone have any good suggestions? I do have the Starrett 260 slot micrometer and another special by Starrett that is similar. It works but only measures the very end of the slot. I do have complete set of pin gauges both plus and minus. Slot height I don't have anything good.Looking for accuracy to .000"

Kurt Learning · Jan 4, 2022

Insert a known block and take up the slack with feeler gauges.

wesg · Jan 4, 2022

Adjustable parallel and a mic. It's probably not really straight anyway. A height master and tenth indicator will show you how much, and the dimension as well.

Froneck · Jan 5, 2022

Having a Starrett 254 height gauge and tenths indicators getting to the location in a 1911 frame is not possible.

sealark37 · Jan 5, 2022

Just asking, why does it matter?

Froneck · Jan 5, 2022

If the trigger moves as a Thompson shaft inside a linear bearing it will contact the disconnector exactly the same way every time. Trigger pull will become stable. One of the most important things in shooting good scores in competition is the trigger. Especially in Bullseye when only one hand is allowed and no additional support to any part of the body, even a wrist watch on the shooting hand is not allowed! Trigger pull weight is limited to no less that 3.5 pounds and 4 pounds when shooting service pistol for the 1911 .45ACP pistol. The 10 ring is 3.36", same target size is shot at both 25 and 50 yards. During slow fire at 50 yards 10 minutes is allowed to fire 10 shots but during Rapid fire at the same size target 25 yards away only 10 seconds is allowed for 5 shots!

kenton · Jan 5, 2022

Cut the trigger guard off, measure, weld the guard back on?

On a more serious note I would probably use gauge blocks and keep adjusting the stack until I got a tight slip fit.

Froneck · Jan 5, 2022

Yes cutting off the trigger guard will be a big help but as mentioned not a very serious proposal. The work required to weld it back on the frame that had extensive accuracy work do to it is not an option!
Yes stacking gauge blocks or fitting feeler gauges can be done but it's a tedious operation being the access is over 2" inside the frame.
Yes I can get it done for myself but you have to understand these target guns cost between $3,500 and $5,500 and more. Not something that one intends to send in the mail. Quite often I get requests at matches to make a trigger so I'm looking for a simple way to test size.

kenton · Jan 5, 2022

Unless something like this will fit inside the trigger guard:
https://www.mscdirect.com/browse/tn...MfCXetBGIAEPNCjqplgaAmzrEALw_wcB&gclsrc=aw.ds

It seems that 2 sets of feeler gauges to measure on either side of the installed trigger may be the most field expedient way. Or make up a set of blocks that cover the normal range of groove widths and take them with you to matches.

Froneck · Jan 6, 2022

I have 2 Starrett and I think 3 B&S and an SPI version of the item linked. Way too big! The 260 Starrett will measure the .250 width. I'll check my Starrett Adjustable parallel 154D to see if it can be modified to fit. If it will I get one to modify because I don't want to break-up my 2 sets of 6.

michiganbuck · Jan 6, 2022

Likely with a one-inch micrometer and a bench grinder one could make a pair of width gauges that would give +- .001 0r better.

Even if one had to finish the last take amount with a file or a honing stone.

CarbideBob · Jan 6, 2022

sealark37 said:
Just asking, why does it matter?

Everything matters.
Do you shoot on or off your heartbeat? That pulse of blood matters.

Froneck · Jan 7, 2022

michiganbuck said:
Likely with a one-inch micrometer and a bench grinder one could make a pair of width gauges that would give +- .001 0r better.

Even if one had to finish the last take amount with a file or a honing stone.

Just how can I do that? I have bench grinders, tool and cuter grinders and surface grinder.

michiganbuck · Jan 7, 2022

Froneck said:
Just how can I do that? I have bench grinders, tool and cuter grinders and surface grinder.

It seems that a piece of CRS might be bent a way that it might fit the slot.. a number of such might be made in increments of -.005 to -.001, and one the target size so taking stock would make a very close fit.

accuracy to .0002" is likely.

The best micrometer will likely not be able to match a custom-made feel gauge.
Yes, check making these with a JoBolck stack... it seems that ringing JoBlocks together might make a decent slot gauge.

Measuring 1911 trigger slot viedo - Bing video

wesg · Jan 7, 2022

Froneck said:
Having a Starrett 254 height gauge and tenths indicators getting to the location in a 1911 frame is not possible.

Tenth Interapid and a long stem will read about 4 tenths per grad. You should easily be able to get to 2 tenths accuracy with a height master.

If you want the trigger contacting the disconnector the same, I'd think the stirrup would be more important than the shoe. The 'Keefer files' show a swaging tool he made to fatten them up for fitting.

Froneck · Jan 7, 2022

I checked the videos in the link, all of them are a waste of time, none had anything to do with measuring the slot dimensions. Only one fitted a trigger but not by measurement but trial each time small amount is removed and that was only one video. In addition he is fitting the trigger with the bow removed! I'll be doing it after the bow is properly installed on the trigger! Used un-anodized aluminum that will form Aluminum Oxide, good lapping material!
I'll see what I can come-up with!
I have seen an item that looks like a spring caliper with a dial indicator, has anyone ever used one?
I see on that Keefer trigger what I don't want to do, stake the sides to increase width! I find that if the trigger is fitted properly the bow is not important other than where it contacts the disconnector. Furthermore I did not agree with Keefer on many things he did!

wesg · Jan 8, 2022

From a pure mechanical point of view, the trigger alone is a horrible guide system. Too tall and short to work smoothly without racking. If I were designing a mechanism from scratch to actuate something with linear motion, that's the last way I'd go.

Better would be smallish contact patches top and bottom, and a 'fit' at the back end where the load is. Locate the tail of the stirrup relative to the disconnector, and the shoe constrains rotation from finger pressure. The contact patches at the front would be better served with hard steel. Either an insert, or skeletonize the entire thing to get the weight down.

No experience with the caliper widgets. The groove things that mount a test indicator work ok for o-ring grooves and such. But either one isn't going to give you any indication of whether the flats are actually flat. A banana shaped slot will measure the same along it's length. Not llkely it's gonna look like that, but ... An adjustable parallel is gonna give you a false reading in that case as well, but the reading you need to fit a shoe with long contact patches.

-cg · Jan 8, 2022

Interapid IRA2 comparator

Brown & Sharpe TESA 079111402 17 Piece Interapid IRA 2 md Comparator Groove Gauge Set, 0.0005" Resolution: Precision Measurement Products: Amazon.com: Industrial & Scientific

Mitutoyo dial caliper gage

209-302 Mitutoyo Internal Dial Caliper Gage: 10-30mm - Higher Precision

Sit down when you look up the prices.

1yesca · Jan 9, 2022

and if you really wanted to take it to an extreme . it would be interesting to have a set of step broach cutters . that would only cut

on one side so you could true up one side at a time by ether shimming or having an over size broach . to do it by hand you almost need

to combine the skills of an engraver , someone that's scrapes machine surfaces and a true die / mound maker . or if you want to lose

the last of what hair you got left set it up in a shaper . or a mill or machine center and use it as a shaper . that is if what you are

looking for is a hole that is true . so that the trigger fits and has an even contact om all four sides . or treat it like a jag hammer

to fit file to finish . for more then likely the slot is not true and if you want it to fit true you have to start off with something that is true .

Froneck · Jan 10, 2022

Simply put I have fitted my Al. Bronze triggers to quite a few frames in Hi end 1911s used in competition. It works great, slides smoooooth and seems to make a difference in trigger pull! Also I do not want to take someone's 1911 that cost $5,500 with out optic sights and begin to re-cut the trigger opening! A simple way to get size in the field is all I want so I can make a trigger to fit the size opening available. I ordered a couple of the type listed by -cg though not the same ones. Yes I can get a measurement in my shop as I have a complete machine shop. But take along items to matches so when asked I can check dimensions also if needed send the measuring tools to the person wanting the trigger.
I want to Thank -cg for the info, using the same description in ebay I found quite a few available in the USA. I liked the one made in Germany but the probes look wider than .250 and no mention as to actual width. Might send question to seller.

Measuring 1911 trigger slot

Titanium

Cast Iron

Titanium

Titanium

Stainless

Titanium

Stainless

Titanium

Stainless

Titanium

Diamond

Diamond

Titanium

Diamond

Titanium

Titanium

Titanium

Aluminum

Stainless

Titanium

Similar threads