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The picture shows a boring head that was among the tooling that came with a little mill/drill that I inherited. It looks to be homemade, and is kind of odd because the moveable part slides on a pair of round pins rather then the usual dovetail. The two boring bars were also in the mix, and appear to go with the boring head. They also look like they were homemade, probably from drill rod. I have a few questions about this thing:
1. I'm guessing that the two locations for the boring bars are there to give a larger range of possible hole sizes than you could get by the sliding action alone. Does that sound right?
2. The two holes for the boring bars are different sizes. One is 1/2" and the other is 9/16". I don't see anybody selling commercially made boring bars with 9/16" shanks. Any idea why whoever made this might have made two different size holes?
3. I have a vague memory of having seen plans for something similar (i.e., a boring head that uses the round pins instead of a dovetail), but I'm not finding it now. Has anybody here seem plans for something like this? The only reason I care about the plans is to see if they might have an answer to question #2.
I think GlennW is probably right. If after a lot of work on the head you screw up a hole it just makes sense to make a few bars that size since the bars were going to be home-made anyway. If you have room, you could bore both holes to a standard size.
I was also kinda guessing that the 9/16" hole might have been a mistake, but wasn't sure. So thanks for the confirmation.
As far as making both holes some standard size, I was thinking about JB-Welding a plug in the 9/16" hole and then drilling it out to 1/2". Any thoughts on why that would or wouldn't work?
rmac wrote: ↑Sat Jan 16, 2021 3:51 pm
As far as making both holes some standard size, I was thinking about JB-Welding a plug in the 9/16" hole and then drilling it out to 1/2". Any thoughts on why that would or wouldn't work?
Not necessary. A thin walled sleeve can be machined and used in lieu of that idea. It need not be split nor even drilled and tapped. That said, there is nothing wrong with the idea of permanently sleeving the bore, but it need not be epoxied in place. Simply make it a press fit, then drill and tap so the restraining set screw can penetrate to the bar. Remember, it is nothing more than a spacer.
The idea of two different sized holes isn't good. On countless occasions, both holes have been used when operating a boring head. It's one way of expanding the range of the head. If you can't transfer the bar from one hole to the other, that may not be possible, and one may not always have a pair of useable bars with both (shank) diameters.
H edited to include the word shank
Wise people talk because they have something to say. Fools talk because they have to say something.
Harold, my Flynn head has 1/2" and 5/8" holes. I can see the benefit of having them the same size, but even if you have to move the bar to the other hole, you would still take a test cut and check the size before before the finish pass, so aside from needing a bushing for the larger hole, I don't see the real downside. I have never used the 5/8" hole(s) with a 5/8" boring bar. In fact, I don't have any 5/8" boring bars short enough to use and my old mill didn't have the Z travel to use a boring bar so long it needed to be 5/8".
whateg0 wrote: ↑Sat Jan 16, 2021 4:33 pm
but even if you have to move the bar to the other hole, you would still take a test cut and check the size before before the finish pass,
Of course you would. You missed my point entirely. I didn't imply that having the holes the same size allows the bar to be moved from one hole to the other without having to relocate the bar in regards to the generated hole. What I said was that by having the holes the same size, the bar can be transferred to the other hole so you can swing a larger or smaller arc, so the same bar can be used to extend the head capability, either larger or smaller. Fact is, that's why there's two holes. If they're not the same size, the bar won't fit, and that was my point.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
You know fellows that this head may have been designed or modified to fulfill a particular application
For example , the 9/16 hole may be for a dowel pin that is used for presetting the head,
In other words, it could be used to center the slide to the quill C/L and that gives the operator a starting position.
Also , the Odd size (9/16) may have been to allow the tool bit to be measured for off set to a even number from C/L like 2.000 instead on 1.968
This would make it a simple adjustment of the location of the boring slide to get a desired bore size and save trial and error
Rich
Many Shop made tooling have these setup enhancement features.
