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Cross drilling

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John Rudd19/06/2017 14:19:00
1366 forum posts
58 photos

I need to cross drill some 3/32 diameter rod, hole will be 1 mm diameter.

What is the usual method for doing this with most accuracy?

Jim C19/06/2017 14:26:36
61 forum posts
4 photos

Hi John, You could maybe mill a small flat on the bar and spot and drill it after marking out in the old fashioned way or indexing across the dia. with wobbler. Or better, you could produce a drill bush from rectangular bar and use that?


JasonB19/06/2017 14:26:42
16573 forum posts
1772 photos
1 articles

Hold in vice with a bit sticking out and use edge finder on either side then half the readings so you are above ctr of the rod, small spot drill then 1.0mm drill.

In practical terms I usually put teh spot drill in teh chuck and pinch a steel rule between that and the work, adjust position until rule is horizontal then spot and drill, really depends what accuracy you need, this is good enough for a thou or so.

John Flack19/06/2017 14:47:42
169 forum posts

I would drill a square section piece lengthways the dia. of the rod,drill a ,cross hole dia vertically through the lengthways hole, couple of threaded holes to clamp, face off one end of the block to give positive location.

Material and hardening to choice and need. Vertically drill hole cut of surplus, piercing saw or Dremel, step and repeat as required

I am a simple soul, there could be very complicated alternatives

John Rudd19/06/2017 15:15:03
1366 forum posts
58 photos

Thanks for the replies....some great ideas there..

I was thinking of the square ( round? ) bar drilled up the centre with a 1mm hole drilled through one face, but wondered about accuracy....I guess the accuracy is dependant on how well made my bar is marked out and drilled...sad

The hole being drilled is in the valve stem for my Webster engine....( yeah....another unfinished I thought I might make some progress with it...

Tony Pratt 119/06/2017 15:17:11
934 forum posts
3 photos

John R,

You have been given multiple options but nobody has asked what equipment you have & how many pieces do you want to drill?

Please advise as it's going to have some relevance to a practical answerwink


JasonB19/06/2017 15:29:37
16573 forum posts
1772 photos
1 articles

If it is only for the pin to retain the spring on a valve then I have used the ruler method plenty of times for that and all the engine run, why go to the bother of making jigs

John Rudd19/06/2017 15:35:11
1366 forum posts
58 photos
Posted by JasonB on 19/06/2017 15:29:37:

If it is only for the pin to retain the spring on a valve then I have used the ruler method plenty of times for that and all the engine run, why go to the bother of making jigs

Yup its for the pin, as for accuracy in drilling the hole, I'd like it to be as good as possible so it looks better than a hole drilled off centre....

Jig wise, probably a bit of bar, with a tapped hole ( m3 ) for a grub screw to hole the valve while I drill......nothing too elaborate....

Equipment wise, I have my 626 mill with dro on x and y, my Sieg minimill, no dro......3 lathes.....

Should be enough tooling there to drill 2 little holes in 2 valves...wink

JasonB19/06/2017 16:08:04
16573 forum posts
1772 photos
1 articles

John why not use the first method I suggested as that is accurate, hold work in mill vice, touch one side with edge finder and zero dro, touch otherside and then use half function which will then allow you to position quill directly above ctr of work and then spot & drill (you would need to do this for the cross hole in the jig anyway)

Jig method can introduce errors, can you get bar running spot on in the 4-jaw, will 3mm hole start dead in the middle, will 3mm hole wander along length of bar, will 1mm cross hole be dead in teh middle and slight clearances on teh holes will allow bar & drill to move slightly. And as for having a grub screw bear on your newly turned valve stemfrown

I know which way I would do it but maybe thats why I get a lot of engines made and don't waste time with jigs or using more accuracy than is needed.

richardandtracy19/06/2017 16:12:28
938 forum posts
10 photos

I have, with a very fine hole done it this way:

  • Saw off a section of the bar, about the same length as your drill bit, put it in the drill chuck.
  • Clamp the drill vice to the bar and then clamp the vice down to the drill press table while the quill is extended by the amount of bar in the chuck.
  • Put the drill in the chuck.
  • Put the bar in the vice and use a tiny file to make a very small flat.
  • Now drill, it'll be pretty well in the centre, the offset being only as much as you deflected the press while tightening things up.

This has worked for me with tubes as small as 1.5mm with a 0.7mm cross hole in a drill press bought from Argos.



Edited By richardandtracy on 19/06/2017 16:14:11

Gordon W19/06/2017 16:16:22
2011 forum posts

I bought a V on a M2 taper. Put in tailstock, with a bit of modding will do for 30mm dia.. Bought from Arc for a one off and now it's the tool of choice.

Roger Woollett19/06/2017 16:17:08
109 forum posts
3 photos

A method I have used involves a custom V block.

Clamp a bit if MDF to the mill table and use the tip of a centre drill (or something else that produces an approximate V groove) to cut a V groove across the MDF. Lock the table so the groove is directly under the mill axis. Now clamp the round bar into the groove and drill in the normal way. I have done this with 1mm rod and a 0.5 mm drill successfully.

John Rudd19/06/2017 16:34:24
1366 forum posts
58 photos

So, have I put the cart before the horse?

I have already made the valves.....methinks this may make the job harder? angry

Shudda ( gone to RadioRentals...) drilled the holes first....perhaps?

JasonB19/06/2017 16:35:38
16573 forum posts
1772 photos
1 articles

I drill mine last

richardandtracy19/06/2017 16:39:01
938 forum posts
10 photos

Absolutely - an interrupted cut can lead to a poor finish.



not done it yet19/06/2017 16:53:12
3583 forum posts
15 photos

have already made the valves.....methinks this may make the job harder?

Practise on a piece of scrap 2.38mm bar first?

Tony Pratt 119/06/2017 16:59:29
934 forum posts
3 photos

Hi John,

JasonB is spot on with his last 2 posts, did this sort of thing in industry for over 35 years.


John Rudd19/06/2017 17:40:52
1366 forum posts
58 photos


I'll let you all know how I get on...( or not...)

Chris Gunn19/06/2017 20:26:52
286 forum posts
16 photos

I always make a jig, it does not take long, I do not bother with splitting or hardening, just a screw to nip the work which can be a brass one if you are worried about marking the work, and if you have a lot to do the jig makes it easy. Over the years I have made a few to suit various diameters, and they are often reused. They are stored in a plastic bin labelled cross drilling jigs next to another marked happy drilling jigs.

Chris Gunn

David Paterson 419/06/2017 23:16:04
83 forum posts
8 photos

Take a short length of brass round and chick in the lathe.

centre drill 1mm about 6 mm deep.

part off , do not disturb in chuck

centre drill through hole 3/32 - ream if you are fussy

set up in vice with 3/32 hole horizontal and 1mm hole resting on the bar - like a laid-down 'L'

1mm hole provides a guide that will be centred. best if you drill right through the brass first then insert the piece you want to put the hole through.

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