Screw Hole Duplication

[walkermaker]

What is the recommended way (simple and accurate to within, say, .002") to duplicate two non-symmetrically positioned screw holes (#6-32) copied from one end of a 1-1/2" x 3/4" rectangular alum. shaft to another identical rectangular shaft when the positions of the two original holes are not known (diagramed)? I have a set of transfer screws (although a standard usage of such will only give the inverse location due to the non-symmetrical layout) and much of the usual shop equipment. Thanks in advance.

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[This message has been edited by walkermaker (edited 07-01-2005).]

[This message has been edited by walkermaker (edited 07-02-2005).]

[This message has been edited by walkermaker (edited 07-03-2005).]

[Carl]

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[This message has been edited by Carl (edited 07-01-2005).]

[Chief Mcgee]

Just thinking out loud here: Wrap a single layer of paper around one of the shafts then place it in a three jaw chuck and clamp the jaws down on the paper. The end of the shaft should be a little ways back inside the jaws. The paper will hold the jaws slightly bigger then the shaft so that you can slip the other shaft (with the transfer screws) down into the jaws and mark the first shaft.

[larry_g]

Lay the bar on your surface plate and locate the positions of the holes with your height gauge. Make a drawing of the locations you found. Alternatly if you can stand the bar on end locate the edge of the bar and the center of the hole note locations. Or take the old bar and locate it with x and y fixed stands on the mll table and indicate the hole centered under the quill, remove the holed bar and replace with new bar, D&T.
lg
no neat sig line

[WJHartson]

Don't know the lenght of the shafts but if relatively short this will work if I understand your question.
Machine the end of the new bar so that it is square and insert the transfer screws in the shaft. Place both bars in your milling vise or other holding device that is known to be square with the ends facing each other. Tighten the jaws so they are just snug and tap the end of the new shaft so that contacts the transfer screws and transfers the marks. This should get you what you want.

Hope this helps

Joe

[Your Old Dog]

make a smoke print of it.

take a small birthday candle, hold the item you want to copy at a 45 degree angle to the flame. Play some smoke on the area. Wait a minute or two and then put some scotch tape on it. When you pull the tape up you will have a positive. If you want a negative, put more smoke on then necessary and then make the one smoke print as normal and then put another piece of scotch tape against the first and then pull them apart and you will have the reverse.

Now if you put a "tiny" half drop of something tacky like varnish on the area you want to transfer it to, rub it with your finger till it's tacky, you can then position the tape over the tacky area and then stick it down and burnish it with the back of your finger nail. When you pull up the tape your image will be there. It works. It's how engravers copy one side of a gun to another side of the same gun. They also save copies of thier work by putting the tape on white paper.

Ray........

[chief]

Old Dog,
I think I understand what you are saying but I don't see where you are going to get any accurracy, especially for locatinga screw hole.

[Your Old Dog]

Chief, you're right! Would take some very careful spotting of the center punch and a whole bunch of luck! The process works for many other similar projects but .002 would be crowding it a tad ;D However, if no other way was available I wouldn't hesitate to give it a go.

Actually, after thinking about it, I don't know if any home process exist that will allow you to mark the work for drilling. Anything you use to mark the work would have more error in the width of the line then .002 . I"m inclined to think it is the more accurate choice of those given with the exception of WJHartson suggestion. If his transfer screws were pointed, I think they would indicate best of the choices given so far IMHO.

edited to add last paragraph:

[This message has been edited by Your Old Dog (edited 07-04-2005).]

[spope14]

I guess I am not getting the picture. If I am getting this right, you are drilling and tapping two holes into the end of a rect. shaft to match another shafts hole locations.

I am going to do this from extreme basics. I do nt know our skill level, so forgive me if I seem to talk down, I am just trying to be complete.

Basicallly sounds like a general locational ,measurement job. I am not familiar with transfer screws, but if they are what I think, they screw into the hole, have a plain diameter up top to measure off of, like pins.

OK, here is what my method would be. The 3/4" dimension will be my "Y" direction - Vertical, the 1 1/2" dimension the "X" axis - Horizontal.

Quick question, and I will check later for follow-up with the most accurate method - do you have gauge pins, gauge blocks, surface plate, and a .001 or better indicator (heck, if you have a caddilac gauge, or a vernier height layout gauge, this is the end all).


Ok, back to it. 6-32 has a tap drill size of #36, or .1065. Your first trick is to find out which drill fits in the ID of the screws. Might be slightly larger, or even smaller. What ever you find, for my example, I will use .1065.

make a drawing of the piece, the X and Y as I mentioned - x is 1 1/2 length, y is 3/4 length. Put a DOT on the lower left hand corner of the rectangle you have made, this will be your edge finding zero, you will make this part on a mill. ALSO, make a concurrent dot on your piece to measure with marker - choose a corner, make this your lower left hand corner.

Put the drill bit in the left most (x axis left) and highest up (y axis highest) on the part screw hole (hole closest to your zero), shank in first, leaving some shank above the surface to measure to. Be sure the shank is smooth. measure from the left edge - edge with the dot - the edge of the 1 1/2 dimension - to the outer edge of the drill using calipers. Example, you find you have .836 length. NOW subtract 1/2 of the drill diameter. In my example, I used .1065 as the drill size. Use .106 as your figure to divide. Always round DOWN in these situations to make up for the slight caliper slant of measuring from edges. Divided by 2, the radius of the drill is .053.

If you have gauge pins, use these and divide the pins by 1/2.

Since you measured from an edge to the outside of the pin/ drill, you subtract the radius of the pin from your measurement. Remmber, I measured .836 (x axis), I subtract .053:
.836-.053 = .783. This is your first hole "X" dimension. Sketch this in on your drawing, and write this down.

Now do the Y axis. measure from the bottom edge of the part - edge with the dot - to the outer edge of the drill shank. For my example, you get .435. Subtract measure and radius of pin / drill as follows .435 - .053 = .382. Write it down on your sketch.....

Your first hole is to center X .783, y.382. Do the same idea for the second hole, measuring from the exat surfaces as you did for the first hole.

remembet the dot, This is the corner to edge find on. Use mill, edge find this as zero, then move to your locations and do it (remember to compensate for edge finding).

This sounds hard, wsh I wre there or had video conferencing, would be able to help you better. It is very easy, very accurate, and a common method in locational finding.

The use of a vernier height gauge, gauge pins, and an indicator will make this better, I can try to describe if you wish.

Hope this made sense. This will get you there.

One other hint, when measuring fom edges to pins with calipers, your calipers "tilt" slightly. Take .003 off your measurements for better accuracy. Also, make sure your part edge leg of your caliper is seated quite well, or you will never get this right.

For complete accuracy in hole drilling, always centerdrill your holes to drill and tap first. Probably sounds quite elementary, but I am more surprised eah day how newbies are not taught this, and they plunge in with sy a #36 drill, and then wonder why the hole is off and tilted...drills walk (go off location in a random direction) unless "spotted" first. You MUST centerdrill, or all that fine measuring and edge finding was for absolutely squat.

I always measure and edge find if I have a mill handy, might lay out for visual checks only - which is an excellent idea anyway.

Feel free to e-mail me.

[walkermaker]

Thanks to all for help. SPOKE14, your method is sure to solve my problem. I do not have a mill (only a 7" lathe) or gauge pins, or gauge block (both of which I will now try to buy). However, with a drill as my pin I am very likely to get by with what I have. I DO have (you asked) a height gauge and a surface plate which blended into your thinking here might increase the accuracy.
Thanks again to you, and all others.