Wanted: Slide fitting advice

[dagle]

I'm onto my 2nd 80% project and already ****ed up.

Made the assumption that a quarter turn would be 0.006" and had 0.048" of total material to cut. I probably made half a turn instead of quarter a few times or something, because when I pulled out at 7 cuts I was 0.006" overcut. After deburring and very light stoning with 800 grit I'm at 0.007-0.008" loose relative to my slide (was aiming for 0.003" )

Anyways I'd like some guidance on methods for getting a super snug fit. I have the slide started about half an inch, but there's interference that stops it. After applying layout dye (dekims) I see that the frame rail's deck's corners are rubbing. Is there a guide or resource that tells what kind of interference causes each mark?

IE: if the rail's show top/bottom marks, the rails need to be widened etc.

My measurements show that my gun should fit together, but it hangs up about half an inch in. How should I proceed? I don't want to blindly lap/file as that's how my first frame got loose/rickety TIA

[InlandViking]

I don't know about any handy guide... But make sure you check the width of the frame. I had to take quite a bit off of the sides of the rails to make the slide go on.. All of the 80% frames I have are wider than the slides I have..

[kcstott]

Knock the corners of the rails, deburr about .010" top and bottom. The bottom of the slot in the slide does not have perfectly square corners. and I can bet that is a good source of your binding.

then double check all your dimensions

[dagle]

I got a little further after posting, the width of the rail on the slide was different at the rear of the slide and in front of the thumb safety cut. It was a .0005-0010" too high. Filed away at that high spot on the deck and got another inch out of it before the next high spot. Majority of the top frame rail is 0.1040" thickness and the slide is 0.1030-0.1035"


How do I deburr 0.10"? I'm not entirely sure what that means. I have deburred via a file at 45 degrees on sharp edges and stoning almost all surfaces with 320 and 600 grit stones

[kcstott]

it's .010" not .10"

Also how are you measuring .0005"? not with calipers i hope? not even digitals. just because it's spits out a number don't mean it's right.

a .010" chamfer 45 degree deburr and i bet you don't have enough. but if your numbers are correct you need more clearance. .0005" to .001" is too damn tight for a 1911

Double check all your dimensions, you have decimals floating all over the place and if you want help we need to know the actual dimensions not what we are guessing you meant.

[InlandViking]

Are you using a Fusion slide? I had the same problem with the slide getting narrower the farther forward I measured.. I have never had that issue with a slide before this one...

[dagle]

it's .010" not .10"

Also how are you measuring .0005"? not with calipers i hope? not even digitals. just because it's spits out a number don't mean it's right.

a .010" chamfer 45 degree deburr and i bet you don't have enough. but if your numbers are correct you need more clearance. .0005" to .001" is too damn tight for a 1911

Double check all your dimensions, you have decimals floating all over the place and if you want help we need to know the actual dimensions not what we are guessing you meant.

Yep, sorry was on Mobile (realized I couldn't edit after posting). I am using a Mitutoyo digital caliper and taking the minimum reading that can be reproduced 5x. My measurements may be off by a thousandth or two, but I will know when my frame is less because it will slide along the frame or at least improve in stuckness.

As far as deburring, I am just doing a few passes with the rail file, then following with probably a 50 passes per corner per stone (320/600/800)

Are you using a Fusion slide? I had the same problem with the slide getting narrower the farther forward I measured.. I have never had that issue with a slide before this one...

No, I am using the Buffalo Stainless Steel slide

[kcstott]

a .010" chamfer equals about .015 face width on the 45 angle.
If they used a sharp tool this should be good enough for the minor radius in the bottom of the slide cuts. If they didn't you'll need more clearance i.e wider face. it's not easy to figure out what material need to be removed.

[bauern]

Are you using a Fusion slide? I had the same problem with the slide getting narrower the farther forward I measured.. I have never had that issue with a slide before this one...

I had similar issue with the last Fusion slide. One rail was narrower by .002" in the back vs the front.

[InlandViking]

Mine was narrower from side to side...

[ar15barrels]

Anyways I'd like some guidance on methods for getting a super snug fit. I have the slide started about half an inch, but there's interference that stops it.
After applying layout dye (dekims) I see that the frame rail's deck's corners are rubbing.
Is there a guide or resource that tells what kind of interference causes each mark?

Its quite common that the inside corners of the slide are NOT completely square so you would need to chamfer/round/break the corners of your rails on the slide.
You want the FLAT FACES of the rails to be what limits the slop, not the radiuses in the corners as the corners will wear much looser than the flats will.Start by breaking the corners.
Then, go to 600 grit lapping compound and lap the slide on to the frame.
After cleaning out the lapping compound with brake cleaner and air, you should have such a snug fit that it needs oil/grease to slide nicely.

[dagle]

Awesome ar15barrels, that's exactly what I wanted to know (where to start and where to end -- lapping).

I presume the route in order of controllability:
deburr corners/edges as described
hand file widths that are too big or too tight
lapping compound

Is it correct to assume that people who lap several thousandths without filing at all (several youtube videos available) generally end up with a sloppy fit because they're lapping areas that have already cleared and degrade the fit with every successive lap? I would think that the front of the frame rail would get lapped significantly more than the back of the rail if you start with the front.

[pklin1297]

dagle, of the steps you've listed, I would flip number 1 and 2. Hand-file where needed, and then break the corners after you're no longer getting marks on the flats.

Sometimes people get a sloppy fit using only lapping compounds exactly how you've described it. Other times, it is because the lapping compounds were not cleaned off completely.

Two schools of thought with using lapping compounds... Some of the big name smiths swear off using it completely on slide/frame fitting, while others think it is necessary evil. Then again, most of them also have nice stout mills that can get the measurements extremely close, so they don't have much filing to do afterwards.

The Purists would have you dykem the rails, knock the slide and frame together, file only the high spots, then repeat, without the use of lapping compounds. Just know that slide to frame fit is only part of the accuracy equation, and not a big part at that... A bank vault, Les Baer-esque fit is bragging rights, never mind that a lot of Les Baer pistols fail prematurely due to satisfying this vanity...

[dagle]

Roger that. I've already messed up the rail so I figured that I would at least get good practice in before the 9mm and 2011 after this.

[ar15barrels]

Awesome ar15barrels, that's exactly what I wanted to know (where to start and where to end -- lapping).

I presume the route in order of controllability:
deburr corners/edges as described
hand file widths that are too big or too tight
lapping compound

Is it correct to assume that people who lap several thousandths without filing at all (several youtube videos available) generally end up with a sloppy fit because they're lapping areas that have already cleared and degrade the fit with every successive lap? I would think that the front of the frame rail would get lapped significantly more than the back of the rail if you start with the front.

If the frame and slide will already slide together with only light force, you are already too loosly fitted to be able to lap them together.

What I do is cut the frame until it measures the EXACT SAME SIZE as the slide.
You should only be lapping the final fraction of a thousandth of an inch.
I lap with 600 grit or 800 grit depending on how tight the slide and frame feel when I start them together.
At the exact same size, the slide will NOT fit on the frame without quite a bit of force because there are always little spots that are too tight.
The lapping will knock down those high spots until the two parts fit perfectly.

The key to lapping is using the correct grit for the fit you are trying to achieve.
If you use too coarse of a grit, you absolutely will create too much space between the parts.
That's the whole REASON that lapping compound comes in different grits.
I bet that many people used the 120 grit "coarse" valve lapping compound because that's what the local auto parts place has.
You have to look a little harder to get finer grits.

Unlike most finishing where you start coarse and go to finer and finer grits, you actually want to go directly to the finest grit when lapping parts together.
If you start with too coarse of a grit, you will make more clearance between the parts than you want.
If anything, start with the finest grit and then go coarser until you achieve the fit you want.
Most people want the tightest fit they can get yet still have free movement of the slide on the frame.
800 or 600 grit will get you there.
Avoid the 120 and 280 at all costs.