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How to drill opposite holes on round stock?

RVJimD

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Active Member
#1
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
 

mikey

Active User
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#4
Tough problem that many of us face, Jim, so not an embarrassing question.

I cannot tell how large the aluminum collar is but there are a number of ways to come at this. I'll give you my thoughts and the others can jump in:
  • Easiest way is to cut a single flat, indicate it flat and then drill before flipping it ... but you don't want to.
  • If it will fit in a collet then collet blocks is the next easiest.
  • You can make a mandrel that locks into the work piece and lock the mandrel in a collet block.
  • You can put the work piece into a 3 jaw chuck mounted on a vertical rotary table.
  • You can try marking a line (with a height gauge) across the end with the work in a v-block, then transfer the lines to the sides and then locate your drilling points. Depends on your tolerances.
Okay, ran out of gas ... anyone?
 

francist

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#5
If you have a toolmakers or drill press vise with the flat sides it could be clamped lengthwise in that and the vise flipped for the second hole. I've also been known to drill a snug fitting hole in a block of scrap wood so that the round part slides in but doesn't rotate around in there. Then same procedure as the vise -- drill one side, flip to opposite face, drill second side. And if the hole isn't snug enough, well, masking tape, hot melt glue, all manner of crudeness abides in my shop to hold things from rotating.

-frank
 

Ulma Doctor

Infinitely Curious
Active Member
#7
a spindexer with a 5c collet would suffice for a mill
a dividing head would provide the very same function
i fab'd a crossdrilling fixture out of my lathes AXA clone 5/8 boring toolholder - a turned shaft, a couple bearings and a small drill chuck- that works well and could also produce the same function
a crotch center in a lathe tailstock could be used
if the shaft was small enough, mount it directly in a lathe toolholder and put a drill in the chuck, drill accordingly
lathe milling attachments
V-blocks and a protractor
that's what i got from the hip.....
 

Silverbullet

Active Member
Active Member
#9
How many holes? If you have a mill and its tramed in , your vise should hold it in line, if it was my job id go thru and not go half way. If you spot the top of the shaft it should go straight. As long as you center the shaft it will stay straight. Another idea, You could mount a bushing the size the shaft fits thru use it to drill thru the shaft by mounting it in a vee block that would keep it from moving while drilling with two vee blocks it would keep the bushing locked but the shaft moving lots of ways to do it but why drill twice if its set up sauare and centered .
 

tincture500

Active Member
Active Member
#10
Ok. Try this. Make a sleeve with the holes placed as you need the sleeve can have flats milled on it. Slip your part into the sleeve and dill your first hole,. Remove the drill and insert a pin to hold the reffeance , rotate the sleeve and part with the reference pin and drill the other side. Seems that this may be a lot of fuss for one part but if your making multiplrss it works well. Tom
 

EmilioG

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#11
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.
 

fitterman1

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#13
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.
 

RVJimD

Active User
Active Member
#14
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!
 

RJSakowski

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#15
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.
 

tq60

Active Member
Active Member
#16
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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Rustrp

Active Member
Active Member
#17
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.

 
Last edited:

Charles Spencer

Active User
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#18
(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
 

Joncooey

Active Member
Active Member
#19
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.
 

woodchucker

Active Member
Active Member
#20
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
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.
 

RVJimD

Active User
Active Member
#21
Here is my solution, I think this was suggested above....

I bored out a tube to hold my part, then milled flats on opposite sides. Then drilled a hole in the center of each flat.



Smaller part installed in the holder while I center drilled the holder.



Gear and axel installed. I think my original hole caused the first one to be off just a bit since the gear is almost exactly the size of the ID , I had to mill a tiny bit of clearance.



Jim
 

RVJimD

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Active Member
#23
The tube ID is only a few thousands larger than the gear, so I milled out a slot for the front gear but that is as far as I got. Since the gear inside the tube is centered, the front gear will need to sit off center. I need to figure out how to make them adjustable and I want to drill out the holes for bearings. Jim
 

Mutt

Active Member
Active Member
#24
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.

This is the coolest gadget I have found in a while. I used to hate drilling a hole thru a piece of round tubing or bar stock as it would always be somewhat off center. This makes it super easy !

http://www.ebay.com/itm/New-Made-in...hash=item20ce0158f0:m:m9Fyr5qKnGTn6IWq4s17j2w
 

BoliverShagnasti

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#25
I broke down and bought and indexing rotary table with 90 deg angles so it holds work flat or at 90 deg. I have to cut holes like this often. My holes are 7/16 and 12.5 mm for a prototype and consecutive versions.

I love this rotary table. I custom cut a 5 inch lathe chuck back plate and fit the chuck to it within .001. Took a long time with a lot of tiny adjustments to cut the back plate, but it is a tool, after all. First I put it in the lathe cut the shape for mounting, then set it on the rotary table.
Then use an end mill on the milling machine to cut it parallel to the milling table. Mounted the chuck and all is good.
When I mic the test shafts cut through through the "pipe" with 180 deg rotation, it is perfectly in center +- .004. This is without machining the stock "pipe" to round.

I was surprised at the accuracy of this table.
http://www.grizzly.com/products/6-Rotary-Table-w-Div-Plates/H7527

I use the Harbor Freight Milling machine and the Grizzly G9972Z Lathe. Both machines I recommend. The Harbor Freight mill has .008 take up in the wheels, but knowing that you can cut easily to .0005.

Before I purchased the rotary table set up. I made a V block jig with a pin at the center. You dril one hole then rotate it and pin it at 180, (pin in a steel angle iron at the vertex). It was OK but could not get it perfect enough.
 

Highsider

Active Member
Active Member
#28
If you do this very often and can drill the material with an electric drill motor, it's worthwhile to make a drilling jig that takes standard drill bushings and is on the centerline of your lathe when bolted to the compound. Then simply dial the workpiece into your 4 jaw chuck, index the chuck by resting a jaw on a metal spacer set on a flat part of the way and drill the Cross hole. If the piece is tubular, you can turn the chuck 180 degrees and index the opposite jaw on the same spacer and drill again.
 

428Bird

Active Member
Active Member
#30
I wanted to make a 1" boring bar for my CXA holder. I don't have a decent drill press or a mill, so I held the bar in the holder. After setting the center height and locking the tool post, I gently pecked away with a center drill to get a good starter hole for the 3/8 stubby drill bit I have. It worked flawlessly.

Britt Bettell


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