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Moving a Hole in Cast Iron

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Steven Volz14/07/2020 06:57:58
11 forum posts
1 photos

I wish to move a hole in cast iron about half a diameter. I have neither the skill nor equipment to braze in a plug and redrill.

What are my options?

Chris Evans 614/07/2020 07:30:05
1745 forum posts

Is it possible to just plug with a tight fitting or loctited plug ? I would plug with cast iron to ensure the drill does not wonder which it could do if you use steel.

Stuart Bridger14/07/2020 07:39:06
476 forum posts
26 photos

I would say JB weld or equivalent epoxy to fix a plug. Make sure you have the recommended clearance to leave room for the adhesive. Surface prep is also key, make sure parts are thoroughly clean.

Perko714/07/2020 07:42:24
351 forum posts
24 photos

Depending on the size of hole, tapping it and inserting a suitable screw with thread lock could be a more secure version of Chris Evan's suggestion. I think plain mild steel would be suitable, anything else could be too soft.

Hopper14/07/2020 08:02:13
4804 forum posts
105 photos

Depends largely on the application. If it's a 4mm hole in a model engine flywheel, it's one thing. A half inch hole in a milling table another. And a one inch hole in a Massey Ferguson cylinder head another. Can you tell us more about it? And what will the hole be used for?

Edited By Hopper on 14/07/2020 08:05:45

not done it yet14/07/2020 08:27:21
5008 forum posts
20 photos

It might be useful to know more details of the problem - thickness, load, blind or through hole, diameter, etc. All may have a bearing on the problem.

Morris Marina hubs have been routinely altered, by plugging and redrilling, to change the PCD from 3.75” to 4” for different sized wheels. Usual, I believe, is to fit a flanged steel plug so that required strength is maintained and redrill on the required PCD . They are plain holes, of course, with the new wheel stud bearing on the flange of the insert.

A threaded insert, as Perko7, would usually be better than a plain plug, I would think?

It might be simply a case of drilling deeper, before fitting a plug, if it is a threaded hole.

Edited By not done it yet on 14/07/2020 08:30:02

Steven Volz14/07/2020 08:41:28
11 forum posts
1 photos

The hole is 1/4" diameter. I wish to move it between half and one diameter. I can't drill it out larger and plug it as there is not enough material on one side of the hole, so I have to plug the hole and redrill half the plug and half the casting, if you see what I mean.

Nicholas Farr14/07/2020 08:52:59
2438 forum posts
1193 photos

Hi Steven, I would go with Chris Evens 6 idea, but use a course thread rather than fine and I would use a medium strength thread locking compound.

Regards Nick.

Clive Foster14/07/2020 09:36:00
2373 forum posts
76 photos

I've used a fine thread with high strength locking compound to do similar which worked fine.

As your hole is going to overlap the junction there is a risk that the different characteristics of the plug material and cast iron may cause the hole to deflect. If you can do so accurately, drilling a small pilot hole first to guide the main drill is good practice. Sharp drill essential. Buy a new one if yours are showing their age and you have no means of doing a really good sharpening job.

Need to keep the temperature down when drilling so as not to hurt the "glue". A sharp drill cuts cooler.

Realistically the exact method isn't of great importance. Quality of work and cleanliness to get good adhesion for whatever "glue" is going to hold the plug in counts for far more. Generally, in this sort of situation where there are a number of options for producing a satisfactory result, the best way for any particular person is the way they are best set-up to do. Whether in equipment, experience or both.

On a rather larger hole I also dutch keyed the plug with a pin set in a hole drilled down the junction of plug and hole exactly opposite the shift. Being a bigger hole I was worried that the plug might shift when running a big drill through. Not something you need to worry about.


Adrian R214/07/2020 09:43:51
41 forum posts
5 photos

If you have the facilities, milling the new hole would be better than drilling as it is less likely to wander off and follow the joint. On a small holes I have managed this with a cheap (i.e. disposable) end mill in my pillar drill chuck which I know isn't good practice but does work.

Dave Halford14/07/2020 10:15:32
921 forum posts
9 photos

Plug the hole with cast iron, any drill or milling cutter will run away from a harder metal and toward a softer one.

Bo'sun14/07/2020 11:59:32
202 forum posts

Yep, a cast iron plug would certainly be the best option. If things go belly-up using a mild steel plug, you could be a lot worse off. Good luck.

Steven Volz14/07/2020 14:31:04
11 forum posts
1 photos

Thanks all.


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