cutting inner barrel windows for er hop

6429 Views 5 Replies 5 Participants Last post by sanguinor, Aug 13, 2012

goldentrigun

Discussion Starter · Aug 12, 2012

This is specifically directed at cheeseman really but I imagine this could be good information for anyone who wants to do a ER hop up.

How do you go about extending the windows of the inner barrel?
My friends idea and mine was to use the grinder which we use to neck back endmills and things of that nature to extend the window. The only problem with that is that they have since changed the handle so it no longer will accept anything longer then 5inches. We could probably ask to have it changed back for a few hours but it would probably require someone else with the knowledge of doing so.

The other idea is to make a fixture and manually take a endmill in the machine and cut the window further. Although we have no ideas on what to make the fixture look like since depending on the barrel it may be hard to clamp it without screwing up the inner diameter.

I'm avoiding cutting the window with a dremel since i have access to a 3 axis machine, grinder, and lathe.

Any help from the people who actually cut their ER hop windows correctly? XD

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careful

· #2 · Aug 12, 2012 (Edited)

Use the mill. The two vertical indexing flats will work well for aligning your barrel. I ended up using an .050" plate pocketed out to an 'I' shape to properly clock the barrel (total place size was only .500"x.750"x.050", it doesn't take much), then parallels to ensure the X-axis was level.

Once that is taken care of, it's very easy to find your dimensions and enlarge the window to your needs. Take it slow, and go with 3/16" or smaller on the end mill, carbide if you'll be working on stainless.

I'm assuming you know your way around a mill, let me know if you need anything else.

EDIT: Don't worry about the vise distorting the barrel, just snug it down, keep the window close to the jaws, your end mill size small, and you won't have to worry about anything.

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woogie

· #3 · Aug 12, 2012

Just use a small flat file.

This way you don't have to worry about over cutting, or messing up the barrel. The file you will be able to take very small amounts off of the barrel.

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Cheese Man

· #4 · Aug 12, 2012

I use a mill and a 9/16" carbide end mill. Make sure you don't cut it dry and you are good to go.

Cheese Man

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goldentrigun

Discussion Starter · #5 · Aug 12, 2012 (Edited)

hmm interesting. I'll have to see about obtaining a set of used alum jaws for my personal use. I'm going to attempt to use the locking pieces to my advantage. I'm comfortable just jogging the cuts it was more of how the hell I was going to hold the barrel as I'm used to milling parts which aren't in the round.

I guess I also need to find a way to hold the hop up chamber as that'll need to get cut as well. Although I think I could do that fairly easily I don't want to spend a whole bunch of time just filing one hop up chamber.

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sanguinor

· #6 · Aug 13, 2012

I do all my cutting with my small files, sure it takes awhile but I get it where I want it

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