Browning Trombone forend screw thread and tap...

A

AikiNut

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So... A little while ago I bought a browning trombone on EE.
Nice little rifle. Cool, someone replaced the fore-end screws with socket head cap screws.
Well, not really. I guess the screws were missing and whoever it was (not sure if previous owner or someone before him) had used JB Weld (I think) to anchor a couple of set screws in the fore-end up against the screw holes in the slide... Discovered that after the fore-end slid right off the slide during the shoot.
So I went to WGP on the way home from the range and got a couple of the proper screws. They're reluctant to start - suggesting that the set-screws may have mashed in part of the threads.
Thread pattern seems to be 0.6 mm pitch, on a screw with 5.0 mm diameter on the un-threaded part, and 4.5 mm diameter on the threaded part.
Doesn't seem to be a common tap size (while I did work in a machine shop for a while, we used pretty standard stuff all the time, making parts for tool-and-die/stamping industry)

I'd like to chase the threads in the slide, with a tap, so these screws will go in properly - anyone know where I can find a tap that will do this job?
 
AikiNut said:
Will look - but made in Belgium?
OK... looks like 40 TPI is the closest I can find. Threaded part is 0.177" OD, not threaded part is .1955
Click to expand...
There isn't a metric thread on a Mauser 98 so where a gun is made doesn't always determine the threads. I don't know in this case, hopefully someone can answer you.
 
guntech said:
There isn't a metric thread on a Mauser 98 so where a gun is made doesn't always determine the threads. I don't know in this case, hopefully someone can answer you.
Click to expand...

Ok. Thanks for trying. I chatted with a gunsmith a number of years ago, who mentioned that a lot of firearms are made with threads in use in the area of manufacture, and they're neither "metric" nor "standard UNC or UNF". Maybe my next recreational bit of reading will be the "threads" chapter in my machinery handbook..edit... nope, that's frustrating too.
 
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You are like to have to make your own tap. Or it will be a custom order deal.

Guns and sewing machines are both full of non-standard threads, and oddball sizes.

I would start with a 'reamer' made of a wedge of soft copper pipe twisted in to the screw holes to clear out as much of the epoxy as can be got, and work from there. Like as not, you can get a decent impression of the threads so as to be able to measure them.

Copper won't make the damage to the threads worse, and it could just be that there is still enough epoxy in there to stop you getting a thread started.
 
i had to replace one on a trombone not that long ago. i didnt have to mke anything special other than shorten a screw. its ether 8-40 or 6-48
 
trevj - thanks for that suggestion - I'll see if I can dig up some copper somewhere.
beater. thanks for that - I'll see if I can search out an 8-40 shcs somewhere and compare it with the ones I bought from WGP. if the thread pattern and diameter works I can "make" a tap from one of the screws.
 
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Resolution: Contacted a gunsmith - he was going to ask for about 140 to clean the threads, and a bunch more to make a tap.
So - I bought another pair of screws from WGP - now I have four... Tonight (I moved in August and a bunch of circumstances have kept me from fully unpacking) I got fed up with hanging about WRT this rifle, and:

Chucked one of the screws into my drill and spun the end on a hone to taper the last couple of threads,
Put a fine cut-off disk on my Dremel and had a go at making three pseudo-flutes on the tapered end of the screw. Home-made "tap"...
Chased the threads in the rifle with the "tap", said a silent prayer to Odin, and tried an un-altered screw.
YAY! The fore-end stock is now held in place, properly, with "factory" screws. I still don't know what the thread pitch is, and now I don't care. Now - to the range to continue testing the wire-cut firing pins and get all of them so they'll go bang...

Hard to believe I didn't even touch this rifle since May, except to move house at the end of August... Tempus fugit (time flies) (Time flies like an arrow, Fruit Flies like a banana)
 
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