[Spiny Norman]

Hi. I'm a newbie on the forums. What an incredible amount of information here! I hope someone can help me.

I have only a small amount of metalworking experience... I just know the basics and that's fine, it's not my main thing (electronics is).

I want to drill a hole with my mini lathe, in three or four different metals, to fit a 12.0mm dia insert into, in such a way that it is snug but not necessarily wedged in for ever.

I have a 12mm drill bit which (as I was expecting) makes a hole slightly too big.. the insert has free play.

Given the cost of decent 11.x mm drill bits, I don't want to buy 11.6, 11.7, 11.75, 11.8, 11.9 (you get the picture) just to find out which works best, if I only need to buy one or two.

So which do you think I should buy?

The 12mm dia (exactly, according to my micrometer) inserts are chromed brass. The four metal rods are about 30mm diameter in aluminium, copper, stainless steel and brass.

Thanks for reading, and thanks in advance for any help.

Norman

[MikeZee]

You need an undersize reamer, available at MSC idustrial supply, for example.
Drill the hole about 11,75 mm then ream thru'.
Experiment with different speeds and cutting fluids as this can affect final size.

Good luck

[Spiny Norman]

That's great, thank you Mike.

Best wishes
Norman

[Crevice Reamer]

You're drilling on a mini lathe? Why not drill undersize and then bore to exact size required?

Boring bar sets are cheap, and a must-have tool:

http://littlemachineshop.com/product...3768&category=

CR.

[Spiny Norman]

You're drilling on a mini lathe? Why not drill undersize and then bore to exact size required?

Boring bar sets are cheap, and a must-have tool:

http://littlemachineshop.com/product...3768&category=

CR.

Genius! I knew something like this must exist, I just didn't know what it was.

Thank you, much appreciated.

Best wishes,
Norman

[Crevice Reamer]

If you haven't watched them already, you might find the MIT lathe training videos interesting:
http://crevicereamer.com/Page_70.html

BTW: Welcome to the Zone!

CR.

[Spiny Norman]

Thanks for the link... and the welcome :cheers:

Norman

[juergenwt]

Buy a 12H7 reamer. Drill 11.7 and ream. Slow with good lubricant. Check. If to loose - stone the reamer lightly with an oil stone.

[Spiny Norman]

I understand that a reamer is that much more accurate than a drill, I just don't understand why. They look to me as if they do essentially the same thing, as far as the diameter of the hole goes.... they are both hard, fast-spinny, sharp-edged things.

I don't get it.

[aucran]

The first time you drill a hole, it will always be over-sized compared to the size of a drill bit. This is from heat expansion and the chips clogging the flutes of the drill.
For holes that need to be more accurate, its best to pre-drill with a slightly smaller drill bit, then drill again to the final size.
If even more accuracy is required, like in your place, a Reamer or Boring bar is used after a hole has been pre-drilled.

A reamer cannot be used to start a hole, it would probably break. Reamers produce accurate holes because the cutting surface (the blades) are ground to size. Also, because of the small amount of material they remove, there is not much heat build up to deform the hole.

[RotarySMP]

Depending on what you are making and what level of accuracy is needed, drills don't make accurately located, round, correct sized holes. They are great at rapid metal removal though.

If you want an accurately located, round hole of a specific size:

You use drills to bring the hole to 0.5 - 1.0mm under sized. This is metal removal. The hole will not be perfectly located, round or straight.

Then bore the hole up to about 0.1 -0.2mm under - this centers the the hole to your lathe spindle axis, makes it round, and straightens it.

Then ream it to size, as reamers give accurate diameter and predictable surface finish.

Running a reamer down a drilled hole won't straighten the hole or bring it back to it's desireed center.

[juergenwt]

Norman- just take our word for it. A detailed explanation would require you to enter a training program and years of experience. No offense please! I like the way you show interest in metal working.