Consistency of Trimmer

[surfclod]

I have been trimming my brass over the past few weeks, I have about 600-700 that have never been trimmed so I get a small batch done every few days.

I am using a Forster trimmer which I am happy with I am just wondering what sort of consistency others are getting with this unit. As I recall there are several on this board who have the same trimmer.

My trim length is 1.840" and it seems pretty consistent (+ or - 0.0015") but occasionally I will get one that drops to 1.837" or therabouts. I set the short ones aside to use for foulers or for some close range brass to play with Barnes 26 gr bullets.

I blame the excessively trimmed ones on operator error but I am curious about what sort of accuracy and consistency I should expect from this trimmer.

thanks

Chris

[Rick in Oregon]

surf: .003" inconsistency is a bit much from my experience with my Forester trimmer. I've seen .001" on rare occasions, but usually it stays within .0015" or better. Check to see if your set screw collar is square to the main body, or if the set screw itself has come loose.

The only other possibility is brass built up on your cutter, and the build-up may be creating a 2nd cutting surface. Improbable, but possible. Let us know what you find.

[Hawkeye Joe]

I can usually get them all within .001 and over 95% within .0005. I use a couple Old style RCBS Collet and drawbar type. I think the Forster is the same. The key is getting the same tension every time when you turn the Tee handle to tighten collet. Less pressure and the case will be short, more pressure and the case will be long from drawing the collet base back creating more space between cutter and collet base. Try positioning the Tee handle in the same spot EVERY time. Finger tight will do just fine. No need to crank on it. Just try to hit the same spot every time with the Tee handle regardless of how tight it feels, (as long as it holds the case without spinning of course ). Another thing to look for is brass chips in the collet and closer taper. Hope this helps.

[Rick in Oregon]

Mike: Good point on the collet....I should have mentioned that. My bad.

[surfclod]

I can usually get them all within .001 and over 95% within .0005.

Actually this is pretty close to what I am seeing, maybe not 95% but definitely close. The few that I did get that were off, I blame on me not making sure that the collet and head of brass were perfectly clean. I also thought that the tension on the collet was important, I even though of adapting my inch/pound 1/4" drive torque wrench to it, but I think that for my use its a bit of overkill.

When I first started I found that the first batch of 50 was all within .0005" but after that I got the odd one that was off. Again I blame these on my error in not making sure all surfaces are clean. I also wonder about some of the brass that I put aside that may not have the face of the head to be perfectly square, this I will check out of curiosity when I have more time. Its only about 15-20 out of the 450 I have trimmed so far that I set aside, so I am pretty happy with the consistency. I was just wondering if I was expecting to much out of my equipment, I'm a welder, not a machinist so I don't really have a good reference to know what to expect.

thanks all

Chris

[acloco]

Don't forget:

Clean the collets - the case head of the brass sits on the step and it needs to be clean.

Oil the lathe bearing surfaces as well - shaft AND the depth adjusting screw.

Oil the handle on the lathe crank, helps keep you consistent.

One other note, run the case head of the brass across some 400-600 grit sandpaper, sometimes the manufacturer/caliber stamp raises quite a bit of metal and this contacts the step in the collet.

[jo191145]

With collet trimmers I found this step helpful.

Along the lines of what Mike said, I put some tape on the trimmer body and on the T bolt. Then a hash mark across them. Line up the hash marks and your brass will be consistent.

If your brass has inconsistent case head diameters you will get inconsistent trim lengths with a collet. If they vary enough you cannot always utilize the hash marks as some will be loose and others too tight.
I ended up with a Hornady trimmer which does not have a collet but uses a shell plate. Now any inconsistency is due to variations in rim thickness.