Reamer question

[lazylathe]

Hi All,

I am looking at starting a simple air engine in the near future.
Was going to be tonight, but materials are lacking...

Anyway i have been reading up on them and decided on Elmers #25.
A simple wobbler.

It says that the cylinder needs to be reamed after being drilled to the correct depth and size.
How important is this?
If it is very important to always ream the cylinder i will need to buy a set of reamers.
This will put off the build for a while longer.

What are the most common/popular sizes of reamers used? If any...

Oh and one more thing...
The drill has a point and the reamer is flat.
Will the reamer also flatten out the bottom of the cylinder?
Another thing i will have to keep in mind when calculating depth for the drill bit.

Thanks and sorry for the noob questions!
I will have a myriad more to come!! ;D

Andrew

 

[BillC]

A reamer will leave a reasonably nice finish if run properly but its primary use is to size a hole. The finish is still needy in that it will require some honing - so you could make a hone that uses carborundum (wet or dry) and hone the bore to size without using a reamer at all. Honing takes some technique to prevent a taper but with a little practice....

BillC

 

[mklotz]

Drilled holes are neither straight, round or the correct size.

Drill to remove material quickly.
Bore to make the hole round and straight.
Ream to bring the hole to the correct size.

In your case, the boring operation will also flatten out the conical-tipped hole left by the drill. Reamers are only meant to remove tiny amounts of stock on the circumference of the hole. Typically, for smaller size holes, the bored hole should be around 1/64" less than the final size before reaming.

A quick way to compute allowance for standard 118 deg. drill tip is to multiply the drill diameter by 0.3 .

 

[peatoluser]

No, reamers aren't used to flat bottom a hole. They're sharpened betwween centres so have centre drilled ends. If you need to flat bottom a hole you can either make a D bit, use a boring tool or if the design allows, just through ream and loctite a plug in.
personly I hate using a boring tool to flat bottom a hole. The screeching noises as i feed in ever so slightly too deep always have me expecting a broken boring tool.
my favorite is the D bit. Easy to make and quite easy to control depth of hole.
The advantage of reaming/drilling straight through is it is easier to lap/hone the hole and keep it parallel.
Hope this helps.

yours
peter

Edit: perhaps i should have pointed out that D bits are used to flat bottom small(ish) holes. typicaly the bottom of ball valve seats. I would hate to have to pay for a 1 dia. piece of silver steel (drill rod) let alone try and make a D bit out of it!

 

[steamer]

Idealy, you drill to remove stock as Marv has stated, then bore to correct the position and make the hole round and straight, but undersize. THEN ream to bring to size as a reamer will follow the hole it enters.

Dave

 

[arnoldb]

Hi Andrew
Good choice for a first engine Thm:
If you can get a smooth surface while boring the cylinder you don't have to ream it; it will work quite well - that is how I did my Fancy's cylinder which is the same size. As Peter suggested, you could make up a D-bit reamer if needed as well; it's easy to make and use.

If you do decide to go for reamers that you want to use for reaming out cylinders, just remember to get machine reamers for that; hand reamers have a long taper on the nose and are not useful for reaming blind cylinders.

Useful reamer sizes for Elmer's engines, and I suspect for most of the smaller engines we build are 3, 4, 5, 6, 8, 10 and 12mm if you want to work in Metric - I just look at the different parts and size to fit where needed when converting. I also keep an appropriately under-sized drill of known good quality with each reamer (2.9, 3.9, 4.9, 5.9, 7.9 9.8 and 11.8m) - makes life much easier.

Regards, Arnold

 

[Tin Falcon]

Keep in mind reamers are usually ether undersize or oversize .
Hole sizes are specified nominal. if you are making a press fit then use an undersize reamer if a running fit use an oversize. A good example is a shaft. the shaft will be nominal size say 1/4 inch.that is fit to a crank disk then though a bearing then into a flywheel.
Tin

 

[Swede]

Reamers are an improvement in accuracy vs. a twist drill, but it'll still make a hole that is not truly round. You can see a flute pattern in the hole after reaming. It should be more than adequate for a steam engine, though.

In the end, as time goes on, I find I use a boring head more than reamers. It is a skill worth learning. A good boring head, some cutters, and the skill to use them, is like having an infinite set of reamers. It's slower, but more flexible in use.