"Grant Erwin" wrote in message
...
DeepDiver wrote:
"Grant Erwin" wrote in message
...

I'm wondering if any of you guys know the bolt pattern of these 4 bolts.
I stuck a piece of steel under there and punched it using my transfer
punches but the pattern is really crooked


Grant, could you explain this? Why would the pattern from the actual
transfer punch marks be crooked? I mean, the holes are exactly where they
are, are they not? So how can the design specs be more accurate than what
you're physically measuring?

Yes, I can explain this. I wanted to transfer the dimensions to a 6x6x1/4"
piece of plate steel, and I wanted them centered and square. The head was
not in a position amenable to one guy working on it, to say the least. I
was able to lift up the front of it and slip the plate in behind it and
set it back down trapping the plate. Then I discovered that my 1/2"
transfer punch didn't quite fit into the holes, so I used the 31/64"
punch. When I got the plate out, the holes were all kittywampus with
respect to the sides of the plate, which isn't a big deal until you
realize that on an engine stand the mount plate had better be pretty well
centered or a top-heavy item will tumble sideways before you get a chance
to clamp it. Plus, there was that worrisome error from the smaller
transfer punch, along with the worry that maybe the plate slipped during
punching.

I'll offer the following alternative solution in the event that actual
published specs aren't available for a future project with similar
difficulties:

1. Get a sheet of material to use as a pattern transfer that's larger than
the mating face of the item in question. The sheet can be a paper product
(like tag board or index card stock) or it can be sheet metal (aluminum or
steel) for more demanding tolerances.

2. Place the sheet under your item so that the sheet extends beyond the
mating flange in all directions.

3. Using either a fine pencil (I like 0.5mm mechanical pencils) on paper, or
a sharp scribe on sheet metal, trace the outline of the mating flange onto
the sheet. If necessary to help see the scribed lines, you can apply some
layout blue first.

4. Now you can use your transfer punches to transfer your hole positions. I
doubt if 1/64" play would matter in an application like this one. (Since
you're using bolts to affix the head to your adapter plate, you need a
certain degree of clearance anyway in your holes. If you're transferring
holes for locating dowel pins, that's another story.) Anyway, if the
wobbliness of the transfer punch concerns you, and you don't have an
intermediate size that will fit snuggly, here's a trick I've used that works
well (although, again, I wouldn't recommend it for high-precision work):
take the largest transfer punch that will fit the hole and wrap it tightly
with adhesive tape to help center it in the hole. You don't want to use a
soft or spongy tape (e.g., duct tape or electrical tape); I've used thin,
clear plastic packing tape with success. It shouldn't take more than a
couple of layers of tape to fill the gap; if it does, your transfer punch is
too undersized.

5. Now that you've transferred your pattern to the sheet, you can use the
sheet to transfer the pattern to your workpiece. You can cut out the pattern
if you wish along the line made around the flange, or you can make centering
marks to align your workpiece on the sheet, or any number of alternatives.
You can work from the front, or from the back (taking into account that the
pattern will be mirror-reversed on the opposite side) as long as the marks
are visible on the back side. (You may want to punch or drill small holes
through sheet metal where the transfer punch marks are.)

Hope this helps.

- Michael