Gunsmithing 10min you'll never get back. FN TBM inlet g-code test, scrap wood

[ken226]

I needed to fit an FN TBM bottom metal in a Manners T4. It took about an hour with a caliper and protractor to write the g-code for the inlet.

Heres the code test run in scrap wood. I use old dulled end mills for test runs in wood. With a sharp 3 flute alu-power the lines in the Manners were perfect.

Sorry i didnt video the actual stock being inletted, but i had some stuff going on so was too busy to video.

It was however, a perfect fit. The TBM setup feeds very nicely in an SPR action.

 

[moosemeat]

Looking pretty good. What is your sfpm on fiberglass?

 

[ken226]

400, with a .003 chip load.

Fiberglass is easy to mill but hard on carbide. The hardness of the glass fibers eats up carbide pretty quick regardless of feed or speed, so i like to let each tooth take a big bite.

I could get away with alot more.

 

[LRI]

It's been my experience that uncoated carbide goes a whole lot better in composites. The coatings often require a bit of edge prep, this effectively "dulls" the tool. Great on ferrous stuff, not so good on composites. The absense of a sharp edge effectively "rubs" the part. As this happens, the epoxies plastisize and bond to the tool. Then you end up with little heat sinks that invite thermal shock. Cutting edge erosion to follow soon after.

I learned this about 10 years ago. Swapping them out has proven worth it. Another good resource is a compression mill. Forcing that chip down effectively acts like a pair of scissors. Crisp, clean edges being the goal.

Good luck. Stock work is always fun. Cedar works great for proofing code. Not so stringy.

 

[ken226]

My experience is the same. I use uncoated alu-power YG-1 mills designed for non-ferrous metals. Theyre great for aluminum and titanium, and as good as i can find for composites.

Thsnks for the tip on cedar. Ill pick some up.

I've never used a compression mill, that sound very interesting. Ill be doing some ordering today, and will pick up some to try.

Thanks for the info!

 

[Alan Warner]

My experience is the same. I use uncoated alu-power YG-1 mills designed for non-ferrous metals. Theyre great for aluminum and titanium, and as good as i can find for composites.

Thsnks for the tip on cedar. Ill pick some up.

I've never used a compression mill, that sound very interesting. Ill be doing some ordering today, and will pick up some to try.

Thanks for the info!

Back years ago when I was inletting a LOT of stocks, I found uncoated carbide to wear out at a rate of about one end mill per stock. Typically a .500
diameter either ball or straight, - 4 flutes.. I bit the bullet and bought diamond coated carbide end mills and WOW!-- I got over 200 times the tool life.
I still have them. Cost was steep at the onset, but savings over time is undeniable.
Alan

 

[ken226]

I ordered some compression and diamond end mills to try.

I appreciate the info.

I posted a Autodesk Inventor solid model .ipt and a A size 1:1 scale .pdf drawing of the TBM inlet profile on Grabcad.com. Feel free to use it if you ever have need of an SPR inlet. Just search for FN TBM. Mine is the only TBM files there.

Its about .01" oversize on most dimensions as the TBM is cast steel and has a little variation in surface straitness/flatness.

 

[Geno C.]

I could use a guy to intel my boys stock for the TBM without messing up the fresh cerakote job....

 

[ken226]

I have a limited number of repeat customers and due to time limitations don't take on any new clients.

Longrifles Inc comes highly recommended though. I would give them a call, hes highly regarded here for fantastic quality.

 

[Geno C.]

I know chad does good work. It’s made very clear on his website though, that it finish of the stock and possible the metal will get messed up in the process and I don’t want to have to recoat it since it was just done

 

[ken226]

It's not possible to guarantee that the Cerakote, bedding block or pillars wouldn't be damaged, or to what extent they may affected.

The stock has to be mounted in a strong steel clamping device, and despite efforts made to pad the stock against damage, cutting forces will be transferred through the stock and into the vise. Anyone doing this type of work will certainly take precautions to minimize damage, and probably could do it with no damage, but making a guarantee isn't possible. Anyone making such a guarantee would likely find himself on many occasions, paying more to re-Cerakote a scratched stock than was made inletting it.

Also, any pillars or bedding blocks will likely have to be milled as well, as the bottom metal has to be mounted at the correct distance from the receiver centerline, and at the correct angle.



The only options are to accept the risk of some minor finish damage, or to keep your current bottom metal. With LongRifles Inc, your risk is probably as low as your going to find. My VMCs work the same way his does and I'm just as likely to scratch the Cerakote.

 

[LRI]

It's not possible to guarantee that the Cerakote, bedding block or pillars wouldn't be damaged, or to what extent they may affected.

The stock has to be mounted in a strong steel clamping device, and despite efforts made to pad the stock against damage, cutting forces will be transferred through the stock and into the vise. Anyone doing this type of work will certainly take precautions to minimize damage, and probably could do it with no damage, but making a guarantee isn't possible. Anyone making such a guarantee would likely find himself on many occasions, paying more to re-Cerakote a scratched stock than was made inletting it.

Also, any pillars or bedding blocks will likely have to be milled as well, as the bottom metal has to be mounted at the correct distance from the receiver centerline, and at the correct angle.



The only options are to accept the risk of some minor finish damage, or to keep your current bottom metal. With LongRifles Inc, your risk is probably as low as your going to find. My VMCs work the same way his does and I'm just as likely to scratch the Cerakote.

This could not have been said better! If I may, I will attempt to expand on it a little more.

The best, sharpest tool in the world will find itself struggling at times on composite stocks. Gel coated ones especially. Gel coat is very brittle and when it chips, it spalls. All too often the edge of a DBM inlet becomes riddled with these types of inclusions. There's no good way to mitigate it either I'm afraid. The problem isn't the machine work, it's the fact that the stuff didn't actually bond to the glass/carbon during the layup. One has to understand how these things are made. You have a cavity mold. Squirt some release agent in them and spray the base color of gel coat. Fingerpaint in your other colors, then start on the layup. Once done you do the other side of the mold. Clam the two together with a big inflatable condom in the center. You apply air pressure to the bladder and it is supposed to push it all into the final shape. For the most part, it works, however its not infallible.

An example: We start with blank stocks as most know. Experience has taught me that the first thing to do is grab a small ball peen hammer and start whacking on your stuff. The idea is to find these voids and issues before we ever get close to a paint gun and finish work. You concentrate your efforts around grip transitions and along show line edges. Anywhere the stock has sharp definition. it's 2x as bad on a carbon layup. The reason is glass is very flexible when wetted with resin. Carbon, not so much. It has a much higher elastic modulus. (I had to look that shit up, lol)

So you do that, then start mixing milled fiberglass and resin to patch up all the booger marks. Sand em down, then you are ready to move onto the heavier work in the milling center.

What this really boils down to is doing the best job you can within the time/price schedule allocated by the client. If I'm capped at $100 for a DBM inlet, there's only so much I can do. Likewise, if a guy is paying us 5 figures to build a rifle, more time can be devoted to little stuff like this.

Great post!

 

[m1match]

My 2003 vintage GAP Rock had a hinged Badger floor plate and no muzzle threading. I sent it to LRI to install PTG DBM bottom metal and thread the muzzle. They did a great job and did not need to recoat the finish.