Drilling a long hole in plastic

G'day.

Here in Oz I am able to participate in rifle shooting competitions.

To clean a .22, a bore guide is advised to keep the cleaning rod from damaging the bore. It is inserted where the bolt normally resides and has a hole through the center to guide the cleaning rod accurately into the barrel.

Having just obtained some Delrin I am wondering how best to make the hole for the cleaning rod (0.20" dia). My first thoughts are to make a 'D' bit. The required hole is about 7" long. I do have a lathe. Any ideas how to do this job?

Regards * Danny M *

Edited By Danny M2Z on 07/02/2014 07:10:48

Hello Danny, I cover my rods in heat shrink sleeving which stops metal to metal contact with the rifle bore. Incidently it does not pay to clean a .22 bore too often, the cartridge has corrosion inhibitors and the bullet lube protects most parts anyway. All I do is clean out the gunk around the extractor and the breech with a sharp pegwood.

Clive

Danny

Drill the plastic rod from both ends, the end closet to the chamber needs to small enough so the rod does not touch it. The other can be bigger if you get a little mis alignment when turning it round in the chuck my commercial one has a hole big enough to get a 30 calibre brush through it the other end is about 1/2" bore.

Olly

To address the drilling of deep holes in soft materials (not in relation to guns/gun cleaning in particular) one way is to bronze weld or silver solder a regular length twist drill to a length of mild steel rod or drill rod to depth required. In use these work fine if you don't push too hard and clear chips OFTEN. In plastics the drill must cut - if it starts rubbing the plastic tends to melt and stick to the drill, then the job stops - usually badly with damage to work or drill or power unit or all three.

Another way is to buy an "aircraft drill" which have a much longer length shank and are HSS 118 degree point metalwork drills. Some hardware stores carry "installer drills" which again are long shanked but usually have a brad point helix grind for wood cutting. If you can find one cheap, in HSS, it could be reground.

Good luck JD

A thought re Danny's original post - does the delrin rod need to be continuous? Could a series of short spacers be fitted like beads over the rod? this would protect the bore just the same as a continuous rod and because they are short they could be drilled with a normal length twist drill say 1 or 1 1/2" deep. Just a thought. JD

Edited By jason udall on 07/02/2014 16:27:14

Hi Danny 0.22 cleaning rods can be bought . Mine is made of 2mm fibre glass with 15mm screwed ends in brass (2mm) which holds brass or fibre bristle brushes or a holder for oil rag ,a handle is fixed on one end

I bought mine but its easy to make them . Clean barrel by pushing from the foresight end ,will not then catch in breech.

happy shooting Maurice

Hi again Danny

.Not 2mm but 4mm .Sorry for that I hate metric!!!

Maurice

G'day.

Thank you for all the replies. I shall try a brazed 5.2mm drill bit onto a stem, otherwise its a 'D' bit.

The .22 is used for benchrest competition, and can put 5 holes in a 10mm group at 50m if it's not too windy.

Apart from cleaning the bore every few hundred rounds (and then re-fouling it with a few sighters), I prefer a polished steel rod compared to a plastic coated one as there is less chance to pick up embedded crud.

To protect the 'crown' (muzzle hole) I always clean from the breech end, and as the chamber (the bit where the shell case fits) is accurately reamed and polished I am keen to preserve it's integrity. Hence my requirement for a bore guide. Since I lapped the barrel, the cleaning requirements have diminished, but inspection with a bore scope shows a build up of residue in the 'throat' (the bit in front of the chamber) after about 200 rounds. This build up does nothing for accuracy.

I know that I could have just asked how to drill a long hole in a bit of plastic, but I thought that a bit of background info might make it more interesting and explain why the hole accuracy is important.

My next project is a barrel harmonic tuner btw, and a bullet concentricity (run-out) gauge is well under way. This uses a Mitutoyo DTI to see how wobbly things are.

Regards * Danny M *

For putting a oily cloth through the bore of my .22, I use a bit of braided nylon cord with a loop at one end, and a lead mouse at the other. I use a 1" x 2" piece of 4 x 2 , .303 cleaning cloth. Ian S C

G'day.

Got on with extending a drill to make my long hole.

Found a nice pre-loved 8mm printer rod, it turned nicely with a freshly honed bit.

Very pleased with the mini-lathe accuracy, I pinched the M3 ER 25 collet chuck from my X2 mill to hold the 8mm rod. 0.210" at both ends of the rod using a travelling steady. Over a 10" length I'd say the tailstock alignment is spot on.

Next drilled the end of the rod 10mm deep to take a spigot. The fixed steady kept things aligned nicely.

Next fitted the 4 jaw and clocked in the victim 0.225 drill shank.

Turned down a spigot on the drill shank to fit the hole in the extension rod.

Tested the fit and eased the shoulder with a fine file.

Fits nicely, left a small gap for the silver solder to flow.

Tomorrow it's time to make an alignment jig and braze the two together. Then attempt to drill a 7" long hole through the center of some 15.5mm Delrin rod.

Regards * Danny M *

Edited By Danny M2Z on 09/02/2014 10:05:58