How to drill opposite holes on round stock?

I was thinking the same thing. A short pin to fit in piece of angle or plate, less wide than the part to fit in a vise
or clamped to the table. The first hole needs to be dead center. A simple, DIY 1018 square collet block with a set screw
would be better for multiple parts.
 
Mikey had it right.
Place stock in vee block. Use height gauge to find center and mark two sides and end. Remove from vee block, stand on end and mark distance from end.
Sit stock in mill table top tslot and use square on end scribe mark to sit vertical. Clamp in this position and drill or drill and tap. Unclamp and rotate 180 degrees, reset vertical line on end, clamp and drill or drill and tap again. Job done.
Using tslots in this manner is timesaving.
Should take you 20 minutes, 30 if you crack a beer.
 
Ha, I like the beer option but I should probably wait till sometime this afternoon to start? ;)

Gona head to the shop now, I'll try a few suggestions and let you see how it goes!

Thanks for the ideas!
 
I use several methods depending upon the desired accuracy.

The easiest is to set up two vee blocks with clearance for the drill between them so the center of the vee is directly under the spindle. The vee blocks can be fairly well centered by laying two parallels in the vee, putting a pin in the chuck and adjusting the position of the block until the pin touches both sides of the parallels equally. Rotate the spindle if you have runout in the spindle. Clamp the vee blocks in position. Remove the parallels, place the part in the vee, and drill through. If there is a clearance hole in the center of your vee block, it can be done with a single block and no parallels. For best sensitivity, I use a 1/2" pin.

For more accuracy, I indicate the fixed jaw of my milling vise with my edge finder and offset half the diameter of the part. Alternatively, if the part diameter is large enough, I mount the part in the vise and locate the position of both jaws and average the position readings to get the center position. This works well with my DRO's as they both have an averaging feature.

In either case, use a center drill or spotting drill and allow the drill point to find its center. This is especially important with round stock as there is a big tendency to slip off to the side.

Finally, if a one off fit for a shaft and bushing, I will sometimes drill the hole slightly undersized, assemble the two parts, and finish drilling as a set.
 
Use a center marking square ...Brain far but adjustable square with the v block in that is used for marking centers on end of round stock.

Mark across end of shaft then place square on table and align scribe on shaft with square.

With calipers mark distance from end.

Center punch or use end mill smaller than OD of hole to make flat before drilling.

Rotate stock and align with mark on end with square and repeat.



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I think it's already been stated a couple of times, and that's the degree of accuracy you want. Milling a small flat on one side as a place to start and marking center. If we are off center then drilling straight through doesn't work. If you don't have a way to index the part then two vee blocks works the best, second to placing the part in a collet block that can be flipped 180°. The centering square works well and two squares together works too, by creating a caliper arrangement (C or U shape). When all else fails I resort to dividing the circumference x 4 on a piece of tape, or grab my pi tape.

I haven't use the method but making a drill bushing the same size as your stock you are drilling works well for one time parts.

See the 4 minute mark and his closing comment on cars vs milling machines is a good point also.

 
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(Please excuse the blur. My old flip phone doesn't do closeups well.)

1. Dykem the end of the stock

2. Put it on a flat surface between two pieces of stock to hold it in place

3. I use a lathe bit ground to a point with the base of the point left flat along the length of the bit

4 Find or make a block half as wide as the stock

5. Scribe a line across the face of the stock

6. Rotate 90 degrees and repeat until you have four scribed lines on the end

7. The lines will either all intersect or they will make a very small square at the center of the stock.

8. It is then possible by eye to punch it within 0.005" of the center

9. Repeat for the other end


scribe2.jpg
 
Might be tedious with small stock but I find the circumference with a tape, (flexible) mark one point, then divide by two and mark the other. Otherwise I follow some version using a centre finder, square, etc. which has already been discussed.
 
RVJimD said:
This is one of those questions that I suspect most are too embarrassed to ask but not me.

How do you locate and drill two holes opposite from each other (180 degrees) on round stock. I am attempting to build a solid rear axel for a Tonka truck conversion with a set of bevel gears in the center as a locked differential.

Here is a picture of the stock I'm starting with.


The first iteration of this I milled a flat on the first side and flipped it over and milled the opposite side flat giving me the 180 degree opposite flat. Then I drilled the holes, but for this one I was going to leave it round.

This is likely one of those things that tomorrow morning it will seem simple, but right now, not so much. I hope this generates an educational discussion. Thanks for the support!

Jim
Click to expand...
Don't know what a Tonka conversion is but I want to see pics when done.;)
Like thequietman said above, if you can't drill all the way thru, a pin stuck in then put the pin in a block that has been clamped to the table where the drill bit comes down on will allow you to meet the 180. Clamp the block, drill it, then , put a pin in the rod, put the pin (in rod) into the block.. It's a real repeatable process.. but the pin must be a tight fit, no rocking so it will have to be a little bigger than the drill bit, since drill bits always drill bigger than there size. You can take a drill (same size) cut it off for the pin, then pound it once or twice (on it's side to create flats and expand the cylinder) on an anvil to create that tightness.. and maybe sand down to get it to fit. It will be more than accurate enough for what I think you are doing.
 
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