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mike thomas
02-24-2002, 11:34 PM
I have been playing with the mill, and I think that my next ebay treasure hunt should be for a boring head. I had little luck perusing Machinery's Handbook. Is there a set range that the various sizes adjust to? Say a 2 inch will bore from X to Y size holes, and so on? I'm pretty ignorant here so keep it simple. Thanks. Mike

Thrud
02-25-2002, 01:07 AM
Mike
It depends on the boring head and attachments. A 3" head might be able to do a 5" hole without attachemnts. When you buy one make sure it has a shank with your spindle taper (R-8?). If you are up to it, there have been articles on "rolling your own". Then again, $50 on eBay sould get you a nice one.

Dave

SGW
02-25-2002, 07:27 AM
Not a set range, as boring heads (the Criterion style, at least) have a hole for mounting a boring bar sticking out from the side of the head. Depending on how long that bar happens to be, and how much free length you can get away with, you can bore a pretty big hole with even a 2" boring head. Probably 4" would be a reasonable limit for a 2" head, but conceivably you could do larger if you didn't get chatter.

I've got a 2" head, and I've always found it to be adequate. It's one of the "high precision imports" from Travers Tool ( www.travers.com (http://www.travers.com) ) and the quality is quite acceptable.

Dave's right -- get a shank to fit your mill. From my experience, holding a straight shank in a collet doesn't work well, as the boring head is a pretty long lever arm and the collet can't hold it rigid enough.

Also be sure your mill can go slowly enough. By the time you get to 2" diameter or more, the surface-feet-per-minute speed gets pretty high even at relatively low rpms.

mike thomas
02-25-2002, 02:25 PM
Okay, I follow you guys so far, but this may sound stupid, but can a boring head go smaller than than the stated size? E.g., can a bar be placed in the bottom hole, or holes, and be used to bore shallow holes? Hey, I have only seen pictures of these things.
The idea of building one sounds appealing, where do I find the directions? Yep, it is R8. Thanks, Mike

Thrud
02-26-2002, 02:43 AM
Mike,
Hell yeah! But to bore a flat bottomed hole may require a different boring bar than is normally sold in the boring bar "sets". That is something you need to consider when you purchase the boring head and boring bars for it. Overhang also becomes an issue with a boring head, so the larger shank bars are better in general (the heads will take only one shank size of bars from 3/8" to 1-1/4" diameter depending on the unit you buy)

Dave

As an after thought it occurs to me to remind you that the boring tool cutting edge must be set to the boring head centerline or cutting performance will suffer as well as surface finish.

[This message has been edited by Thrud (edited 02-26-2002).]

SGW
02-26-2002, 08:03 AM
Yes, the boring head size dimension is just the diameter of the boring head. You can put a weeny boring bar in any of them, and bore as small a hole as the boring bar will fit into.

I'm pretty sure there were plans for a boring head in some back issues of Home Shop Machinist. There have also been plans in Model Engineer from time to time, but I think the HSM plans are probably your best bet.

mike thomas
02-26-2002, 02:08 PM
Thanks guys, I can wing it form here. Mike