D bit reamer help

[Seanol]

I cross posted this in another forum and I am looking for some advice.
I am trying to get some info on making a d bit reamer. I have G. Thomas' two books but I have a need for some clarification on some points.

I need a .250 and a .375 reamer. If I purchase drill rod (or silver steel) will it be sized correctly? Could I turn a larger piece to size and hope to get close? (tough question since you have no way of knowing my capabilities I know...)

With the stock the right size I believe the text indicates removing about .001 to .003 material past center and grinding about 7 degrees of clearance. At that point I am thinking that I will heat to a non magnetic state, plunge into water straight up and down. Polish and heat to a straw color at the tip and stone an edge.

Is it that easy?

I know that 2 reamers are relatively inexpensive but SWMBO will not cut loose any funds for toys. The use for these reamers is to ream the holes on a conrod for a .60 Crusader engine I am building. I can get to within .001 on turning usually but I am worried about spring of the work piece and I don't think I can grind a boring bar that small.

I am excited if it works out because I do like the idea of making tools instead of buying them. I just don't want to bite off more that I can chew and I have no way to currently measure a bore that small accurately.

Thanks for looking,
Sean

 

[tel]

Yep, it really is just that easy. Opinions differ on just how much to take off - I aim for exactly 1/2 diameter (tho' I've been known to make 'em 'arf a thou off one way or t'other) and they work for me. Angles aren't real critical within reason - I usually put a bit of rake across the front as well - mainly for making ball seats.

Just stone the flat - don't attempt to stone on the material of the diamer.

 

[Florian]

Hi Seanol

Making D-bits is really easy.
I usually take a piece of silver steel with the required diameter or turn it down to what i need (if there are no silver steel rods available with the required diameter).
If you only have a big not very accurate lathe you can use a dial gauge to turn it exactly to the required diameter (control with the micrometer screw)
And now, harden the rod before you remove the half part of it! (otherwise the rod will distort because of its unsymmetric shape)

Then gently grind away one half (you need to watch out not heating it up too much otherwise it will loose its hardness)

Last step is sharpening it on a sharpening stone.

If you grind away a little more than a half, the "reamed" hole will be slighly less in diameter. So if your d-bit reames too big, you can grind away a little and try again. You can also make a chamfer on one side and then ream with that side. (using oil then!) This also makes a slighly smaller hole...

Florian

 

[kvom]

Unless you are interested in making the reamers for their own sake, I am willing to loan you mine for the price of postage (and promise to return them ;D).

 

[vlmarshall]

Unless you are interested in making the reamers for their own sake, I am willing to loan you mine for the price of postage (and promise to return them ;D).

I was just thinking the same thing! ;D

 

[Loose nut]

You might have a problem with your method.

To use a D-bit properly and get accurate results you need to bore the beginning of the hole to start the D-bit, same ID as OD of d-bit , to a distance slightly greater than the cut away section of the D-bit otherwise it will not start straight and your hole will be off centre and or over sized. With a small con rod you don't have the length to do that?

Better off with a regular reamer or careful boring. If that's not an option then there are other types of reamers you could make that might do the job

 

[Seanol]

Gentlemen,

Tel:
Thanks for the drawing and the info. I think I might go that way.

Florian:
If I leave the blank oversize by .010 would this be enough to machine first and grind after? If not I will try it by grinding after. My idea is to use the lathe with a dremel in the tool holder to get back to proper size.

kvom & vlmarshall:
Thank you for the kind offer. I am thinking that making this tool will open up areas of this hobby I could explore by learning some of the old techniques. My idea is to drill to a close size and ream about .005 off. I wil use the mil and a collet for accuracy. The material is aluminum so I hope the hole will follow the existing through hole and if I am off a little I will hone to size. What other type of reamers can be made for this?

Is this a recepie for failure? I am reamimg a through hole for a distance of .375. I can always try to grind an old end mill into a boring tool. I have a couple that sacrificed their usefulness in the pursuit of feeds and speeds... :big: :big:

Thank you,
Sean

 

[Florian]

Hi Sean

It depends on how you design your d-bit.
I'll make some photos of my newest d-bit, so you can see how i make them.

What can be said in general is, that you should use a D-bit like you would use a reamer.
This means if you want to ream to 4 mm, you should use a 3,9 mm drill.

I also make a chamfer on the front, just like a "normal" reamer has its ingate.
Also i slightly counter-bore before i ream.

Ecept, if i want to make a ball seat, i make some special d-bits...

Florian

 

[Seanol]

Florian,
Pics would definitely help along with a how-to of the process. While my hobby money is tight I am enjoying thinking outside the box and hope these skills will allow things I previously couldn't do.

Regards,
Sean

 

[bearcar1]

All of the above and it has been my experience that the drill rod/silver steel is sometimes not exactly to specs. being usually a few thou' oversize. Something that would make the entire exercise of making a D-reamer useless. Personally, I would use a true reamer and rest assured that the hole is true to size as well as round. It's just me.

BC1
Jim

 

[tel]

Making D bits is a useful skill, and well worth mastering - you can make 'specials' for all sorts of things once you know how.

That said, it's as well to keep in mind the first principal - it is easier to make an OD dead to size, than it is a 'ole. SO ..... make your hole first, and the pin to fit.

 

[Florian]

Hi Sean

Here are the pictures:

Thats a D-bit for making holes that measure 3,90 mm. But it depends on materials what size the hole in the end will be. For example if you ream bronze, the hole will be smaller than in brass because bronze is tougher than brass.
Anyway.. here the pictures:

And here you can see the chamfer on one side of the flat: If i ream running the d-bit backwards (means the chamfer "cuts") the hole will be smaller than if i run it "forward" where the "cutting edge" "cuts"

I also made a chamfer on the front to center the d-bid when starting:

I grinded the flat and the front chamfer with a little selfmade toolpost grinder. Thats why the surface is slightly curved. Though it looks scratched on the pictures, the surface actually is glassy.
I wanted to remove the annealing color but also didn't want to destroy the important parts of the D-bit. So i just stopped doing it

Florian

 

[Seanol]

Florian,
That helps alot! I will have to hold off on this for a little bit as I broke my last insert and can't find anymore! But I will post my success of failure when I get to it in a week or two!
Thanks again,
Sean

 

[Florian]

Oh by the way:

Silver steel rods can be purchased as ground to tolerance.
I don't know if the tolerances are defined exactly the same all over the world but if i buy silver steel rod i buy the ones ground to h9 or even h6. When using these rods, you should not have any problems with variances any more

Florian

 

[lugnut]

I don't know where I got this, and I hope it is usable. When I looked at this post something rang a bell and I looked into my collection of usefull things and found this:

Hope it helps
Mel