View Full Version : Proper way to open up a sizing die on a lathe

05-06-2010, 04:08 PM
How do I open up a Star Sizing die .001". I have access to a lathe. He said he was going to make a rod, attach some sandpaper, sand it to the proper size. Does that sound like the right thing to do?

05-06-2010, 04:28 PM
Yes, smooth sandpaper, 320 or 400 wet or dry. Remember, only .0005" needs removed from each side.

05-06-2010, 06:56 PM
The lathe is a superior way to do it. If I had access to one that is how I would do it. I used a nail with a slot for emery paper in it. Go slow and check your work. .001 isn't much.


05-06-2010, 08:07 PM
I've got a lathe, and I do it by hand anyhoo. Buckshot described a method where he wrapped sand paper (I always use 400 grit - it gets smoother as you go) around a dowel and put it inside the die and rolled it back and forth on his thigh. I saw a slit in the dowell, and chuck it in a drill and insert (while turning) it into the die and open the chute. Insert it from the top (entry) end and any tapering will improve the die anyway. As long as you're only opening up a thou (or maybe two), the hole will still be straight and round.

05-06-2010, 11:11 PM
What your machinist friend is describing is a hone. There are a few ways to make them. In general the stiffer the better.

For opening up a hardened die you'll either use a hone or a grinder. A grinder would be overkill on a simple size die. If you need to polish the lead taper you can turn a hone with whatever angle you need.

It all sound easy until an armature tries it. LOL. After you've done it a few times it's actually easy to master.

If all you need to do is polish a size die you can use a wood dowel close to die size. You'll use this in a drill. Hand or bench top. If the dowel is a little fat spin it up and file or sand it down to desired diameter. Then you can either use super glue to attach a strip of fine abrasive cloth or cut a slit in the dowel to insert your cloth. Wrap around until you achieve required diameter. You can easily measure the cloth diameter with calipers then tear it off at the point where it's correct diameter. Wet with diesel fuel if you're paying for it or WD 40 if your boss is. Then just spin it up using the familiar in and out motion to keep die walls parallel although you won't get much material removal. About 800 grit paper to get a polish. Coarser and you'll have a larger hole. I use finer to finish then a few lead slug laps with 1200 grit compound once it's in the sizing machine.

Once you get them polished “good enough” count on the next fifty thousand boolits to finish the job. If your die gauls up with lead you didn't polish it “good enough” and you get to start over.

05-07-2010, 12:32 AM
I've use the lap method to open up size dies. Using a boolit with lapping compound. I've had good results and I've ruined a couple of dies with distortion. Bit of luck is required. Leftiye suggested a sound method with only hand power. I always like a motor on it. Do see an advantage to his method in that you would not need to fit the hone to the bore diameter. Fine for hobby work. But when I got payed to make chips I'd of been shown the door pretty fast if my boss saw me rolling a part back and forth on my pant leg. LOL. Unless I was doing it as secondary work while a CNC machine was running full tilt.

Using the rolling method you'll not have any ability to enhance concentricity of the die. Which is often an issue with the junk that shows up in my mail box. A solid hone will knock off the high spots first.

05-07-2010, 02:20 AM
If you have access to a lathe.......make an expandable lap of the proper size and lap the die out. Then save the lap. You can use it again or loan it to someone. Use the opportunity and the access to the lathe wisely.......I think a properly sized lap is the best way to go on a hardened die.

05-07-2010, 07:13 AM
Use an adjustable brass barrel lap with lapping compound. Finish with 400, 600, then 800 grit emery rolled onto a small diameter rod.

05-07-2010, 03:33 PM
Keep in mind when you "Lap" by any method it gos fast! You are only talking .001 so basically turn it on 3 or 4 seconds and stop and check. If it was me and I just wanted to remove .001 I wouldn't use any grit heavier than 400 especially since you have no experience doing it. Just my opinion.

Good luck.

05-07-2010, 09:35 PM
And ya gots to clean it out good before you measure it with a (use a) PIN GAUGE or you'll get a false reading (and ruin the gauge).

Doc Highwall
05-07-2010, 09:46 PM
To check the size put it in your luber sizer like you are going to size it but don't turn the ratchet handle for lube pressure, instead take one of you bullets and put some bullet lube on it by hand and some on the inside of the die then check the size of the bullet with a micrometer for a more accurate measurement.