Filling holes

Hi,

I am looking for advice on filling 4 tapped through holes in cast iron.

I am renovating a Stent T&C grinder, some of which is built really well but other parts have misaligned and drunken tapped holes. Once I have filled the holes I will need to tap new ones within the filled areas. I envisage boring (method unknown) out the existing 3/16" BSF holes to a diameter that will more than encompass the M5 replacements so that all of the new threading is within the plugs.

Do I

1. press fit some MS plugs

2 push fit and retain some ms plugs

3 countersink either side of the plate and fit the plugs as rivets

4. tap eg M10 and retain the threaded plugs

Once in place I'll flush them with the existing surface

I can fill them with weld etc as this would probably distort the casting which is surface ground.

All ideas gratefully received

Tony

Fill the threaded holes with a matching thread, cast iron if you wish, retained with Loctite. Drill tap and flush off once plugged, you will not notice the "repair"

Hi Tony,

As they are through holes I would be inclined to drill through to clean the thread out - and, as they are drunken, preferably using a slot drill to true the bore if the depth is not longer than the cutter - then counter bore the lower face about a millimeter more on diameter for a short depth. Turn up 'top hat' pre tapped bushes a reasonable fit and assemble with Loctite finishing off as you say. If you make the bushes from CI and don't deburr the holes before fitting the bushings after cleaning up the faces the joins will be near invisible. The top hats can be though drilled or blind

This method works well and is very strong with a minimum of 'attention to fits' required.

Hope this helps

Regards- Ramon

I manged to drill out of the side of a part that took two evenings to meet.

I'm not worried about distortion, but is it practical to fill a 5mm dimater hol, open along one side, with arc weld?

Neil

I would like to know why Ramon Wilson recommends counter-boring to fit top-hat bushes; why not plain parallel ones?

As the flange on the top-hat is on the underside it stops the bush being pulled out by the M5 fixing.

J

Neil, what material are you talking about, with reference to filling with arc weld.I have been known to fill a hole in steel plate with MIG weld and it was not a very small hole, neither was it that big. Ground off afterwards and you could not tell.

If the errors in the parts are sufficiently small ...I would recommend fitting HeliCoil thread inserts.

The finished job should then be better than "as designed".

MichaelG.

As Michael says, because the thread pitch of M5 and 3/16 BSF are in essence the same, the M5 being 0.24mm larger in diameter, then you should be able to true it up to M5 if you guide the drill & tap perpendicular to the surface and get a good thread.

Personally I would tap M5 or M6 and use M5 or M6 bolts.

Another alternative is, if the design will accommodate a stud and nut arrangement rather than a bolt and threaded hole, then you can tap the hole M6 and make a stud M6 one side and M5 the other.

Nigel

I would true up the holes and tap for helicoil inserts. We often do this in aluminium as standard to give a good thread surface where bolts have to be in and out on a regular basis. I certainly would be the quickest solution.

regards Martin

Tony,

As an aside ... there is a useful article about the Brooks-Stent, on the GadgetBuilder website.

However; noting that yours is Cast Iron ... this article may be of more interest.

MichaelG.

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Edited By Michael Gilligan on 25/10/2012 09:08:37

Edited By Michael Gilligan on 25/10/2012 09:14:16

On the repair/ rebuild I'm attempting on a ST no 9 steam engine one of the 4ba holes for a stud in the front of the cylinder was stripped,and was about 4 mm, so I tapped it 10 32 (3/16) UNF, and made a stepped stud, ie 10 32 one end, and 4ba the other. In your case, I would drill and tap a suitable size, thread cut a bit of cast iron, or brass, even steel would be ok, and loctite it in place. Ian S C

Hi Kwil,

I''m not 100% sure what it is - Its a slice off some random 5/8" plate, but it machines like an unleaded mild steel.

The drill came out the far side and marked the jaw of my cheapo drill vice. That means its a trough that I can't tap or plug. I need the new hole to overlap, so filler is put of the question.

It's a tangential tool holder to fit my QCTP (a brilliant idea I ought to have patented!)and the hole for the clamp to hold the tool in place was the last operation :-0

If it's dry tomorrow I'll have a go at welding. I'm banned from welding and brazing under cover now after buring a hole in the side of a mop bucket and putting my wife's bike at risk. A bit harsh, I feel, it's not like I welded the dog to something.

Neil

Edited By Stub Mandrel on 26/10/2012 20:59:28

Hi,

Thanks to all who contibuted. I will go with the top hat solution. Luckily once the mating parts are in place the repairs will not be visible. I have no access to helicoils nor experience and unfortunately the existing holes are so far out that realignment and tapping thru the 3/16 to M5 is not possible either. However these are good solutions & I will bear them in mind for future corrections.

Thanks also to Michael for the links to the Stent articles. I am incorporating some of the modifications described by Charles Woodward in MEW. I have the Z axis completed and will soon start on the Y axis. My mods also incorporate metrication.

Tony