flat bottom holes

[cessna]

Hi, I am using aluminum heads on my Hoglet, I have drilled undersized holes for the valve guides, I want to put cast iron valve seats in, my question is what is the trick of drilling flat bottom holes to press the seats in? I have tried to make a D bit as per instructions in MEB mag but no matter what I do to the bit it chatters and squeals with very little cutting. Any suggestions would be welcome.
Terry
I just found some posts on this topic, will give them a try.
Thanks

 

[bearcar1]

Dean (aka Deanofid) has an excellent how-to article on making your own counterbore cutter posted on his website. You may want to take a look at it and have a go. If nothing else, it gives a good look at techniques that could be utilized for other procedures.

BC1
Jim

 

[kvom]

Using an endmill might be a simple solution if you have the correct size

 

[rake60]

I use and end mill that is 1/16" smaller than the hole diameter.

The remaining .032" corner left has never caused a problem for me.

Rick

 

[Deanofid]

Terry, what diameter cutter, how fast are you turning it, (or the work piece), how deep, etc.
Some details, and I know we can help you.

Also, see my current build, about page 4 or 5. I show how to make a piloted cutter to cut a flat bottomed hole. Check my website for countersinks if you like, too.

Dean

 

[Julian]

Hi,

My last flat bottom holes several weeks ago were drilled almost to depth with a normal drill. Depth was measured to the POINT of the drill. I then flattened the end of the drill on the grinder and drilled very slowly with cutting paste and squared the bottom of the hole. I find at slow speed this works well as you are only removing a very small amount of metal. Only do it in the mill, lathe or drill press so all is clamped well down. Kept the trashed drill to one side for next time.

Julian

 

[Blogwitch]

I invariably use a slot drill if it is the right size, but if not, then a d-bit has never failed me.

I would suspect your d-bit isn't quite correct somewhere.


Bogs

 

[DickDastardly40]

I concur with Julian, drill the hole to depth with a standard drill and then open the cone out at the bottom. I didn't catch what diameter you are workng with.

Perhaps you could try your D bit on the cone to save having to custom grind a drill.

Another thought if you have a boring head with a small boring bar you might be able to flatten a pre-drilled hole with that.

 

[cessna]

Thanks for all the help, much appreciated, I think I will put the heads in a four jaw and use a small boring cutter. The holes need to be 1/2" diameter, an end mill would work great but unfortunately my little Sherline wont handle it.
Terry