# Inexpensive and accurate reamers



## steamer (Jul 4, 2010)

Hi all,

Those of you who are new and need a reamer for a "few holes", only to find they are $20-$30, take heart.  Check into "Reamer blanks"

They come in all sizes, are cheap, and can be easily made into a very accurate reamer by hand on a bench grinder.

These blanks are of HSS.  Grind a singular flat at an angle of 1 in 5 on the side.

Clean the burr off....a touch of scotchbrite works well here.

That's it.

Drill to a few thousandths undersize, take a very light boring cut to straighten the hole, and then run this reamer through.

Because it only cuts on one edge, you will need to keep you stock removal small...a couple of thousandths......005" max.

Case in point, I needed to make a mounting bushing for a pinion on my son's RC car. The OD of the bushing was .125 and the bore was 2mm.

Standard reamers are $20. (MSC)

I bought (6) 2mm reamer blanks from McMaster Carr at $1.53 each.

Fit perfectly!

Here's a sketch







Dave


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## Tin Falcon (Jul 4, 2010)

Dave:thanks for the tip and the drawing 
Tin


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## bearcar1 (Jul 4, 2010)

Nice easy tip Dave, thanks.

BC1
Jim


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## shred (Jul 4, 2010)

These things (I've seen them called 'toolmakers reamers' elsewhere) are super-handy, especially for making close fits for shafts and drill-rod-- chop a length off the very shafting, make into a reamer and you get a really nice fit. If you sand down the drill rod a little before hardening, it makes a good press fit.


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## Twmaster (Jul 4, 2010)

Do you need to harden these before use?


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## steamer (Jul 4, 2010)

H





			
				Twmaster  said:
			
		

> Do you need to harden these before use?




HSS ...no

Making your own with drill rod.....with Aluminum and perhaps brass....ummm no

cutting Steel....yes

Draw the cutting edge to a light straw color.

Dave


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## Troutsqueezer (Jul 4, 2010)

Hi Dave, 

For us newbies, when you say "take a light boring cut", what does that mean exactly? I ask because the boring bits I have are too big to bore a 2mm hole. What tool or bit would you use for that?

-Trout


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## steamer (Jul 5, 2010)

Troutsqueezer  said:
			
		

> Hi Dave,
> 
> For us newbies, when you say "take a light boring cut", what does that mean exactly? I ask because the boring bits I have are too big to bore a 2mm hole. What tool or bit would you use for that?
> 
> -Trout



The boring cut is to correct for the inevitable wander of the drill.  They all do it to some extent leaving you with a wobbly hole (run-out).  The reamer then follows this hole, leaveing you with a nicely sized wobbly hole.

The correct way to take care of this is to drill undersize, then bore to a few thousanths under the reamer size with a single point tool. That will correct any run-out from the drill. Now you have a nice straight hole to run your reamer through. Problem solved.

With small holes, I generally I wouldn't use the boring bar technique here....ream the bore and then make up a stub mandrel a good fit to the new ID.  Then bond the part on to the stub mandrel with cyano glue (Krazy glue) and turn the OD concentric to the bore. This is a clockmakers trick.

However, 

Making a boring bar this small is definitly "doable".....and I would start with a reamer blank! ;D

I'll sketch one up and make one......but not tonight...I've turned into a pumpkin.

Dave


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## Tin Falcon (Jul 5, 2010)

tell us Dave what are the advantages and disadvantages of this design over the "D" bit. i would think the d bit is a bit less grinding but hitting the exact mid point would be critical. 
Your style more suited to a shop without a surface grinder.?
also this one not useful for blind holes. 
Tin


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## steamer (Jul 5, 2010)

Tin,

Right on all points

A D-bit would need to be ground to just before centerline.. (there are various opinions on before centerline, on centerline and after centerline....if it works for you it's right ) This doesn't require that finesse

If your going to ream to the bottom of the hole, I think a D-bit is better, for small holes anyway. A good case here would be a check valve seat which is usually and inverted cone.  A D-bit is a must here

The beauty of this style , IMHO, is the ease of manufacture without any special equipment..."by eye" will get it done.....just grind it easy once the tip gets thin so you don't burn it.  Grinding to a sharp point isn't really required either, and I have made some that didn't come to a point.

For a straight through hole, I think either way will work fine, and both methods could start with a reamer blank.

I also have a "hybrid"...my terminology...in mind...I'll try it out and report

Dave


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## shred (Jul 5, 2010)

Here's a Colin Binnie dissertation on the subject-- intended for small live steam loco builders, but probably applicable otherwise


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## steamer (Jul 5, 2010)

Actually, My hybrid is half way between #1 and #2.........with a front relief to cut to the bottom of the hole......we will see....I have kid duty at the moment...and the honey do list..


Dave


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## steamer (Jul 5, 2010)

OK

1/4" OD drill rod x 2mm ID about .300 long

I first drilled to .076....or .0025 undersize.

I then made up a boring bar as shown in the photo's below

Sketch






Boring bar with reamer and finished part.







The boring bar is made from a .0625" reamer blank. I ground the top and side to a pie wedge shap, then I releaved behind the cutting edge for clearance. I then mounted the bar into a piece of 1/4" round stock with loctite. The 1/4" round shank gets the tool at least near center of the work, and lets me rotate the bar so the top of the cutter has the proper rake with respect to the work.

I mounted it in my QCTP and with a 8" ring light with a magnifier, I got it as on center as I could...checked it for clearance with the hole, set my feed into the slowest one I have and then started the lathe and set the speed to about 1800.

With the magnifier ( about 10X) I very slowly fed the tool until I could see it touch....I fed about .0005" on the cross feed dial ( .001" on diameter) and hit the power feed.






















Once through, I set up my sensitive drilling attachement. The photo's show it below. It's a very good (Bison I think) chuck with an Albrect shank mounted on MT3 Arbor with a hardened steel drill bushing. I carefully bored it for a press fit such that the arbor has no perceptable shake....smooth as glass. To feed, you use you fingers to push the chuck into and out from the work. If the drill starts to grab...just let go and the chuck will spin with the work...good for taping too.











Anyway, I set up my attachment with a toolmakers reamer and reamed it through











It can be done.  Smaller than this and I would need better optics to do it though
Interestingly enough, MSC sells carbide boring bars for holes down to .020"

http://www1.mscdirect.com/CGI/NNPDF...819010&PMITEM=09155987&PMCTLG=00&PMT4TP=*LTIP

Dave


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## Twmaster (Jul 5, 2010)

Thanks Dave what a great tutorial!


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## SAM in LA (Jul 6, 2010)

Dave,

Thanks for the schooling.

I learn so much from the posts on this forum.

Thank you,

SAM


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## xo18thfa (Jul 6, 2010)

Dave. Thanks a lot for posting this class. It just goes to show that you don't have to spend a ton of money to have quality tooling. I will give this a try. 

And thanks to Shred for posting the Colin Binnie lesson.


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