Jig-drilled holes 1/16″ out – plug, slot drill or replace?

[William AyerstParticipant @williamayerst55662]

I could kick myself – I made a Harold Hall fixture/drilling jig for the Stuart 10V, and used this to drill the holes in the base plate. Though in one axis they are spot on, in the other (longitudinal) there's about 1/16" out – presumably because after all the faffing to centralise in one axis the other had shifted.

The holes are drilled through the jig at tapping size (No. 45 / 2mm) but need to be opened to clearance size (No. 39 / 2.6mm).

I see my options as follows:

1. Leave them as they are, offset the standard's bolt holes by the same amount
2. Drill out offset, to clearance size either by filing holes oval first, or using a relevant slot drill
3. Drill out in-situ, over-size (i.e. large enough that the standard's holes could be in a normal location, and pass through enlarged holes in the soleplate, being fixed with washers/nuts underneath)
4. Plug the gap (with what?) and re-drill more accurately through the jig
5. Buy a new soleplate (and may as well do the standard if I'm doing that – as I overbored that) and start over

All of this is very exciting and my morale is very high – I'm learning so much from my mistakes it's hard to be upset – but I'm not sure how to approach this and would love to hear any advice.

Many thanks,

[William AyerstParticipant @williamayerst55662]

[Ramon WilsonParticipant @ramonwilson3]

Hi William, resurrected a few mistakes in my time so the following is based on doing the same thing! – It should be relatively easy to achieve.

If you have previously deburred the holes drill them out a size to remove any witness of chamfer then plug the the holes holes using small cast iron plugs if possible mild steel if not. Put them in with Loctite retainer and gently peen the protrusion to swell the plug to the hole. Mill or fill of flush. Removing all trace of a chamfer will eliminate any witness.

Set your drill jig up again and align with existing correctly positioned holes. Move to the correct location of second holes and drill through using a slot drill that will encompass the previous incorrectly placed hole. Turn two small top hat plugs that will fit these holes and drill through these with your tapping drill. Loctite these guides into your jig and redrill the component through them. Open the holes as planned but better would be to make these top hats with the clearance drill size so that they help guide the drill through the plugged area.

 

Hope that helps you – Tug

Edited By Ramon Wilson on 07/06/2021 14:02:03

[Howard LewisParticipant @howardlewis46836]

For what my advice is worth,

Drll out well oversize, and tap.

Make up a solid bush and screw into place, using an anaerobic retaining compound.

File / mill / turn plug back to flush. If you are really good, the boundary between parent metal and bush may be almost invisible!

Will the baseplate stand a tiny skim, say 0.002" (0.05 mm), for this?

Give the jig the same treatment, to bring the holes back to where they should be.

Redrill holes in the bedplate, using either the rectified jig, or if you have a mill, by co-ordinate drilling. If one hole is in the correct position, use this as your datum point, and work from there.

HTH

Howard

[JasonBModerator @jasonb]

For this particular situation where the surface won't show I would use a 3-flute milling cutter or slot drill to make a decent size hole in the correct position say 5mm dia and then tap it M6 x 1.

Then make up 4 custom studs from 6mm dia material turning one end down to 2.5mm and threading 7BA and thread the OD M6.

Simply screw the M6 end of the stud into the M6 hole and drop the other part (drilled 7BA clear) onto the studs and use nuts to retain it, better than supplied bolts anyway.

Edited By JasonB on 07/06/2021 14:52:49

[RedsetterParticipant @redsetter]

I take it the misplaced holes in the baseplate are those for the screws holding the standard? If so, your method 3 is simple and practical, and it is not really worth plugging and re-drilling the holes.

The important thing is that the standard has to be aligned with the bottom end of the engine.

If you make and fit the crankshaft, bearings, con rod and crosshead, you can use the assembly to position the standard correctly – drill the standard first, offer up, then enlarge your base holes accordingly. The screws will usually locate the standard adequately, but if concerned about this you could insert a couple of dowels from underneath.

However the most complicated solution is usually preferred on this forum, so others will disagree!

I have built 3 Stuart 10s to a good working standard without any jigs, and so have a great many other people.

 

 

 

 

 

 

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Edited By Redsetter on 07/06/2021 15:13:32

[William AyerstParticipant @williamayerst55662]

To be clear, the holes in the jig are spaced and set correctly – just that the whole jig was shifted along the longitudinal axis by 1/16" – so the holes are correct with reference to each other, but shifted with respect to the baseplate they're drilled into.

For visibility, I've marked and scribed absolute coordinates onto the surface and you can see the shift (bottom-left is lense distortion, I think)

I can't seem to find anywhere to get cast iron plugs – any ideas for supply?

Synthesising the approaches suggested: I think my first step is going to be to slot drill them out at the correct coordinates to 1/8" with a slot drill. That will be a sloppy fit (+20 thou over 'clearance' )  for a 7BA stud but might be OK. If not can open the now correctly aligned hole using a No. 30 bit, and tap 5BA then make some double-ended studs as recommended by Jason B.

 

Edited By William Ayerst on 07/06/2021 17:59:05

Edited By William Ayerst on 07/06/2021 17:59:16

[Ramon WilsonParticipant @ramonwilson3]

When you plug a hole using a threaded plug you wil lalways see where you have done it – the helix of the thread ensures that.

In my book unless you bring the original back to spec everything else is a compromise – depends on how one wants ones work to be seen I guess. 'A mistake is a mistake' – we all make them – disguising them (or not) is down to the individual.

Good luck with it William however you reclaim it

Tug

[William AyerstParticipant @williamayerst55662]

Ramon, if you have any ideas where to get cast iron rod suitable for the job then I'm all ears. I had read that you don't want to plug with dissimilar metals as when drilling you'll end up having the bit drift away into the softer one?

[JasonBModerator @jasonb]

Just get some Cast iron bar 1" or bgger and saw say a 1/4" slice off it. Then cut that into 1/4" strips and hold in your 4-jaw so you can turn to the required diameter.

Another source is the chucking pieces you get on castings which can be saved for making small items or even saw up a spare/spoilt casting if you have any.

[Ramon WilsonParticipant @ramonwilson3]

Sorry William – I just assumed your base would be cast iron as the two Stuart Tens I had were. Just turn up some brass or bronze plugs and do the same – the tighter the better – and reposition the holes as said before but make sure that jig is in the right position and can't move or – lay out the hole positions using the mill – find the centre lines and work both ways.

It's worth bearing in mind if a mistake is made it's never a good idea to make the matching component match – now you have two parts that are in error and sometimes that 'error' continues to throw up further problems down the line.

My thought is very much put it right first then continue but as always it's always down to individual choice.

 

Tug

 

PS as I looked at you image I thought your base is bronze – maybe not. Jasons right if it is CI any little scrap of iron can be turned up but Mild Steel would be just as good – once painted that will be out of sight.

 

Have to go out now – hope this helps some – Tug

Edited By Ramon Wilson on 07/06/2021 18:29:02

[JasonBModerator @jasonb]

Ramon, he is doing it all on the lathe, no mill or drill press.

[Ramon WilsonParticipant @ramonwilson3]

Well that puts a very different light on matters Jason – I well remember my own not so successful experience of being in that situation oh so many years ago.

I still think the best advice is to plug the holes and realign the jig in the correct position. Much better than trying to make the mating part 'fit the error.'

I admire your outlook on this William and wish you every success with it.

Tug

[William AyerstParticipant @williamayerst55662]

Jason, I've managed to get myself a pillar drill – which is what I used to spot through into the baseplate with

I've ordered a replacement standard and baseplate. I'm going to try to fix what I've got, but I think you hit the nail on the head Ramon – I don't want to perpetuate the errors (alignment-wise) – so if that ends up unavoidable I've got a failback position. It feels like it might be a bit of a cop-out but in reality I've spent about £100 on drills and a slitting saw + arbor, so it felt churlish not to spend £28 on castings.

I like the use of the Harold Hall fixtures and clamps for their convenience but I'm just not sure about using them as a blind jig. I'll double check all the measurements before using them again, for sure.

[William AyerstParticipant @williamayerst55662]

Well, my enlarged holes milled to the correct position were fine – but the holes on my standard are out in exactly the same way. I was using the same bloody jig so I can only assume my drill guides are out with reference to the scribed alignment marks.

On the bright side, I did practise boring out the standard and that, at least, worked.

I think I'm going to throw this particular jig in the bin, though.

[Ramon WilsonParticipant @ramonwilson3]

William, when making any jig or fixture the tolerances should always be better than those on the part for which it is intended.

A drill jig is usually designed to be used from one side only so in this instance it will be fine for drilling the base but unless drilled through the jig from the opposite side of the jig not suitable for the standard.

With the limitations you have it may be better to drill the standard first – the tapping size drill – then clamp that in position and spot through just one of the holes. Drill and tap that hole then open the relevant hole to clearance size in the standard and bolt the two together in alignment. Reclamp (don't rely on the bolt) and repeat the process for the other three holes.

You may have to make an extension for the spotting drill – much quicker and easier than a jig – to get down beside the standard.

It's not a bad idea to approach making parts on using them to give you the accuracy required for the next part

Hope that helps some – Tug

[William AyerstParticipant @williamayerst55662]

Well I am very pleased – second time around both the baseplate and the standard turned very well, including the boring process which I took VERY slowly and methodically. I'm following the 'How to build a vertical steam engine' book, but using Harold's fixtures where appropriate (i.e. to machine the standard feet).

I am wondering if I will need to get some transfer punches or whether it will be good enough to eyeball…

[JasonBModerator @jasonb]

Just use the drill bit that you drilled the initial hole with to spot the location onto the other part as Ramon describes above. This was the standard way to do it before many makers got mills and DROs. Run it slowly in your drill or even turn by hand if you just want a mark to pick up. You can also make up your own transfer punched by turning a point onto a suitable diameter, probably have to do that anyway as bought sets tend to be 1/32" or 0.5mm increments so won't be a good fit in holes for BA fixings

Don't eyeball.

Edited By JasonB on 14/06/2021 08:26:05

[William AyerstParticipant @williamayerst55662]

Thank you Jason – good shout, I don't know why I said "eyeball" !!!

On the note of boring/etc. I had to grind down my 8mm HSS boring bar right down for it to fit. I thought a 5/16" carbide bar would be a better bet but it seems to need a hole that's already > 5/8" – is there a rule for determining the size of hole required based on some dimension of the bar?

[EmgeeParticipant @emgee]

Posted by William Ayerst on 14/06/2021 08:51:59:

Thank you Jason – good shout, I don't know why I said "eyeball" !!!

On the note of boring/etc. I had to grind down my 8mm HSS boring bar right down for it to fit. I thought a 5/16" carbide bar would be a better bet but it seems to need a hole that's already > 5/8" – is there a rule for determining the size of hole required based on some dimension of the bar?

The width of the cutter head will determine size of hole it can be used in, usually boring bars have a reduced shank size at the cutting end.
So if the head will enter the hole you can more than likely use it to bore.

Emgee

Edited By Emgee on 14/06/2021 11:40:58

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