Close fitting hole

[cfellows]

Back to working on an injector pump for a model hot bulb engine. The pump body is made of brass and the plunger will be a 3/32" drill rod. I don't have a 3/32" reamer and on my first attempt, the plunger fit is a little sloppy. So, I'm looking for ideas on how to make a close fitting hole about 1/2" long in brass for a 3/32" plunger. Any ideas?

Chuck

 

[Jasonb]

Make a reamer from a bit of your drill rod. Cut the end of teh rod at a shallow anglesay 15degrees and file smooth, harden it and then stone the surface.

Drill a hole just under 3/32" and then use your "reamer" to finish the bore.

Jason

Edit somethiong like this
http://www.homemodelenginemachinist.com/index.php?topic=9854.0

 

[jonesie]

i would drill the hole .005 to .010 under size, then on the 3/32 drill on the cutting edge stone a small flat area on the cutting edge and the use it will cut like a reamer. try on a piece of scrape first. i have had good luck doing this jonesie

 

[ksouers]

Chuck, I've gotten a nice close fit on 3/32 rod using a #42 drill. Don't know if it will be close enough for your needs, but it worked for me on a rod bearing. I DO have a 3/32 reamer and the fits seem comparable, both deliver a free sliding fit on a piece of ground stainless that mic'd out at .0932.

 

[steamer]

Jasonb is spot on....I would clean the bore with a boring bar before reaming it though...cleans up any drill run-out.

Dave

 

[Blogwitch]

Chuck,

Before going any further with this, please check to see whether drill rod is the right material to use.

If there is any doubt at all that water, even in minute amounts, will be able to get to it. Drill rod used in pumps has a very bad tendecy to corrode very badly, with disasterous results, just like when it is used in model steam engines.

As a personal recommendation, I would go with a piece of ground stainless.


John

 

[steamer]

I agree Bogs...missed that part....for a one off hole in brass, you may be able to use stainless as a reamer, as is in it's soft state....worth an experiment on a off piece I would say.

Dave

 

[cfellows]

Tried using a piece of 3/32 drill rod with a 15(+/-) taper ground on one end for a reamer. Stoned and cleaned off all the burrs. When I used it in the reamer, it created a hole with a noticibly sloppy fit. May not have drilled the original hole big enough and tried to take too much off with the reamer.

Chuck

 

[fltenwheeler]

When I worked on big injection equipment we would lap to fit.

http://www.mcmaster.com/#expandable-laps/=89j853

You can also try burnishing. Press a hard 3/32" ball bearing though the hole.

Tim

 

[steamer]

Hi Chuck,

If the starting hole runs out, a reamer will try to follow it. Unless it floats at the tailstock the reamer will end up moving in cone as it trys to follow the hole run out....end result a bell mouthed hole.

Drill undersized, bore to about .002 undersize to straighten the hole out, and then ream it....it will work better.

 

[radfordc]

Drill undersized, bore to about .002 undersize to straighten the hole out, and then ream it....it will work better.

What tools and techniques are required to bore a .090" hole?

 

[Lakc]

What tools and techniques are required to bore a .090" hole?

A teeny tiny long boring bar.

A reamer is your best bet here, but burnishing is a method I have been meaning to try.

 

[steamer]

What tools and techniques are required to bore a .090" hole?

Like this tooling.

http://www.homemodelenginemachinist.com/index.php?topic=9824.msg108782#msg108782

That was a 2mm hole... .079"

Dave

 

[Blogwitch]

It is dead easy to make a tiny boring bar.

1/16" drill ground across the end with an angle of about 10 degs,with the flute at exactly 90 degs. Use a pin chuck to hold drill, hold pin chuck in your toolpost at a slight angle so the side face of the drill doesn't touch the side of the original hole, only the ground flute at the tip touching. See C-o-C

Very high speed, very slow feed.

Bogs

 

[steamer]

It is dead easy to make a tiny boring bar.

1/16" drill ground across the end with an angle of about 10 degs,with the flute at exactly 90 degs. Use a pin chuck to hold drill, hold pin chuck in your toolpost at a slight angle so the side face of the drill doesn't touch the side of the original hole, only the ground flute at the tip touching. See C-o-C

Very high speed, very slow feed.

Bogs

YUP!....
It works VERY well everyone....don't be intimidated by size....its just big parts in small scale. ;D

Dave


on edit....not how I made mine....see post.

 

[cfellows]

Interesting Bogs, never would have thought of that. I also picked up a couple of 3/32 reamers on Ebay. They should arrive in a couple of days.

In the mean time, I ordered some tiny chromium balls from smallparts.com. I bought 1/16 and 1/32. The 1/32 are really tiny. I'll likely use the 1/16 for this project.

Chuck

 

[cfellows]

I tried burnishing yesterday, pushing a 3/32 ball through the hole. I first drilled the hole out with a #43 drill. I didn't have anything to drill the hole bigger without going oversize. I put oil in the hole and tried pushing the ball with a 1/16" piece of drill rod in my 1 ton press. The ball went down relatively easily for about 1/4" but then wouldn't go any further. The initial hole was drilled all the way through, so I'm not sure what stopped the ball.

Chuck

 

[SAM in LA]

Chuck,

Is it possible that the ball galled to the hole? ???

SAM

 

[mu38&Bg#]

#43 is simply too small. I was pressing some 3/32 rod into holes I drilled with a #43 drill and this was not a practical way of doing it. It tore aluminum out the other side every time. I was thinking about getting a 2.3 or 2.35mm drill.

 

[cfellows]

On my 4th attempt, I finally got a nearly perfect fit. I drilled it out with a #43 drill, then used Bogs' suggestion of making a small boring bar from a 1/16 twist drill. Using my mini-lathe, I bored out the hole, taking about a .00025 cut per pass. The graduations on the compound are pretty large and I backed out the boring bar 1/4 of the distance between marks on each pass.

I got the hole to the point where the 3/32 plunger would barely start into the hole. Then I used the tapered boring bar I made from the same material as the plunger, pictured below, and and slowly reamed out the hole by hand. Then I finished reamed to the bottom of the hole, again by hand, using the d-bit reamer pictured below, also made from the same length of 3/32 drill rod. The plunger now has no detectable side play at all, yet slides freely in the hole.

I'm pleased that it worked, but it was definitely a slow process! This injector pump has a .046" hole in the bottom and will use a .0625" chrome steel ball for the check valve. Not used to working with tiny stuff, so it's a bit of a challenge!

Chuck