Flat bottom holes.

[KevinM]

I am building Elmer Vernburg's beam engine and I need to cut a 1/4" diameter, 1 inch deep flat bottom hole in brass for the cylinder. Am I going to have to bore it? That seems that it would be quite a challenge for me. Are there any other solutions that will make the hole and have a very smooth walls?

Elmer's engines are now in the public domain and can be found at http://www.john-tom.com/html/ElmersEngines.html. A lot of other content is available on the site.

 

[Liljoebrshooter]

2 flute end mill

 

[NC Rick]

The endmill won't be real flat. Finish with a counterbore with a removable pilot? I'm not sure how flat is needed.

 

[KevinM]

I am not sure that the 2 fluted endmilI will leave a smooth enough wall finish and probably cut oversize. I am not sure how flat the bottom needs to be. I could possibly drill a little deeper and ream to final diameter without a loss of power/performance.

 

[Bi11Hudson]

The end mill will leave a better wall finish (rounder) than a drill. And not as good as a reamer. The bottom will be reasonably flat, especially as compared to a drill. If the mill is long enough for what you are doing. . . Drilling ahead with a slightly undersize drill and using the mill like a reamer would give the best results. Drilling over depth may prove detrimental depending on . . .

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[benmychree]

I would drill, flat bottom drill and then ream with a near new machine reamer with little end chamfer. Remember the need to dub off the cutting edge of the drills to avoid "hogging in".

 

[KevinM]

3/6" end mill and step ream to size?

 

[benmychree]

3/6" end mill and step ream to size?

1/16" stock would be too much for a reamer that size.

 

[mikey]

You don't mention your tolerances. If the hole has tight tolerances, has to be straight all the way down the bore with a good finish and a really flat bottom then boring it would be the best way to do it. Given the depth and closed bottom, you are looking for a positive lead solid carbide boring bar.

 

[KevinM]

Benmychree, I meant 3/16". I have number and letter sets of reamers. I just tried a test with the plunging end mill and it left a much better wall finish that I expected.