Question on milling slide for Hybrid barrel

[msg73]

Can you use a single end mill to cut out the slot for a Shuemann hybrid barrel (e.g. is the hybrid/port base semi-circular)? If so, what size end mill would you need?

[Matt Cheely]

Yes, you can use a 7/16" endmill. I would rough out the slot with a 3/8 first, then run the 7/16" in there.

[Toolguy]

If you only use the full size one first it will pull to one side and one side will be ragged and oversize and one side will be ok. If you rough out most of the material first with an undersize endmill, then use the full size one to do a light finish cut, it will turn out a lot better. You may want to go down the middle and then an additional .015 or so on each side with a 3/8 endmill to minimize the amount of material that the finish cutter has to remove. Stay short of the end with the roughing cutter and ease in to the end with the finisher.

[msg73]

Thanks. I agree on the rough cuts first...I was mostly concerned about the end and wasn't sure if it was a semi-circle or some sort of partial oval/curve.

[Zoomy]

Like was said, rough with a 3/8" end mill. If you can get a 7/16" end mill that has a first regrind around .420 diameter will get you closer to finished size. Also be sure to go all the way to the full length of the slot and then machine back out to remove any deflection. Then with the 7/16" size end mill first go to the end position and slowly plunge down to finish the radious portion then lift up and go to the start position and lower the endlmill leaving a minimum amount of spindle exposed to maximize rigidity. Now machine the slot to the finish position and then back out again to take out deflection and ensure the slot is centered.

[Can]

you will be better off spot drilling the exact center of the radius in the back of the slot , then drilling it out with a 27/64ths drill or smaller, that will rough more of the material out and have the radius in the back of the slot in the correct place. then your 7/16ths end mill wont squeal so bad, and have as bad of a finish. Also rough the rest of the slot out with a smaller end mill because it will flex toward the side of the slot that your climb cutting on. (and smaller end mills are much cheaper)

to everyone else, hi, i'm jeff i'm new, this is my first post but im a long time machinist making high end aviation parts.

[Toolguy]

Welcome to the Forums Jeff! Where are you?

[Can]

seattle area.

The way you told him to mill that slide, is the way I would do it. But i find newer guys have a harder time with it. it's easier for them if they can just drop the smaller endmill into an existing hole and mill outward knowing they are still undersized on the slot especially with no digital read out(dro).

btw, i would also probably cut a block to fit inside/under the slide, so when the end of the slide is cut away your vice does not squish the slide distorting it's shape...preferably aluminum so it does not matter if you cut into it.

*on second thought it should be stout enough that's not necessary. never mind.

Edited September 14, 2015 by Can

[msg73]

Excellent tips. Thanks guys.