Bellcrank Extension-Boomerang hole size questions

[dgrapes59]

I have a question about the pdf file that was recently shared for the "boomerang". I was getting my son to make me one at his work's cnc plasma cutter. He had a question on the hole quantity noted and that led to a discrepancy on the sizes noted (if I'm reading it correctly).

Three of the holes on the boomerang and 1 block are .565, which is for 9/16" bolts. Shouldn't this be sized for 5/8" bolts? (And 4X)
And the larger hole at the end and 1 block is .688, or around 11/16", shouldn't this be sized for the 3/4" dowel pin on the rockshaft? (And 2X)

Thanks.

[Bill V in Md]

I believe you are correct. The hole on the end (through the boomerang and backing bar) should be sized for the 3/4" dowel pin on the rockshaft. All the other holes should be sized for a 5/8" bolt. The total number of holes called out in the drawing dimension notes (6) includes the number of holes that must be made in both the boomerang and backing bars.

[Jim Becker]

My original notes for the sketch say the two holes with the spacers are 13/16 and the two others are 11/16. Typically IH sized holes 1/16 greater than the corresponding bolt.

[Don McCombs]

Corrections noted.

[Jim Becker]

I took a look at a live part and found things not quite as I had said previously. First off, this is from notes I made at the time of the original sketch:

The part is made from 2" wide by 1/2" thick stock. I would suggest starting with a piece longer than needed and cutting off the excess after it has been bent. The inside radius of the bend is about 1 1/2 inches. The line at the upper right of the trace that looks like a stray line is the actual end of the part.

The 2 rectangles around 2 of the holes are spacers that are welded to the main part. The upper right one is 1 1/2 by 2 1/8. The other is 1 1/2 by 2 1/16. They were probably designed as identical parts. They are 5/8 thick. The 1 1/2 dimension is aligned across the main part, so they don't reach to the edge of the main part. They are welded on the 2 sides near the edges of the main part, but not across the ends.

The diameters of the holes, starting from the upper right, are: 13/16, 11/16, 13/16 and 11/16. Holes 1, 2 and 3 need to line up with the holes and pins of the rockshaft arms. The fourth is 3 1/2 inches from the third hole.


Jim Becker 3/30/00

The new inspection doesn't happen to be the exact part I measured back then, but I don't think that matters. I found the holes not to be as large as 1/16 over bolt size, but still notably larger than the corresponding bolt sizes. The real kicker is the third hole (second one with the spacer) that I had previously reported as 13/16. The actual measurement depends on which end of the hole you measure. That hole through the main boomerang is the smaller size, about 11/16. But the spacer welded on at that hole has the larger 13/16 hole. Evidently, the spacers were all made the same eliminating the possibility of a small-hole spacer being welded on at the bigger hole.

If you measure hole diameters from the spacer side, you find 2 holes each size. If you measure from the outer side, you find 1 larger hole and 3 smaller ones.

[dgrapes59]

So, it appears I would be safe telling him:

Size the one hole at the end, with the backing block, including 1 backing block, slightly larger than 3/4" (.78?). The remainder of the holes and one backing block slightly larger than 5/8" (.65?).

Does this sound logical?

He's cutting it out with a high tech cnc machine, so won't be any bending needed.

Thanks,

[Jim Becker]

That should work.