Castings problem remedial advice, please

[Cornish JackParticipant @cornishjack]

I recently purchased a set of castings for a Tiny Power twin. The previous owner had started to machine them and has made a bit of a bodge of it. The standards have been drilled (bored?) but off-centre, such that the ‘skirt’ of the trunk guide has been reduced to approx. 0.060ins on one side and 0.120-0.130 on the diametrically opposite bit.

Question is – would it make sense( be possible) to sleeve the whole thing with a piece of brass tube Araldite’d into place and then mill this out to match the original side openings?

Alternatively, would it be asking for trouble to leave dimensions as is and accept that it is asymmetrically set up? … both standards have been machined to similar dimensions and would match in offsets when mounted to the base plate.

Final alternative – order a new set of standards

TIA

Bill

[Cornish JackParticipant @cornishjack]

[Ramon WilsonParticipant @ramonwilson3]

Hi Bill,

 

I certainly wouldn’t try to work around the error. That will mean compensating for it on all other parts and inevitably lead to complications further down the line.

 

Sleeving the bore by ‘gluing’ in an insert using an epoxy based product or the relevant Loctite and then remachining to bring it back to print is an acceptable alternative. You could also soft solder it in though personally I would prefer the adhesive method.

 

I’m not familiar with the ‘Tiny Power Twin’ but assume these castings are ‘bronze’ as you mention using brass. Any hint of a join line in the side openings can possibly be disguised by painting.

 

New standards should definitely be the last resort

 

Hope this helps – Ramon

[JasonBModerator @jasonb]

I’m not sure what material the cross head is made from but I would sleeve with bronze or gun metal as it has better wear properties than a brass sleeve would and as Ramon says loctite would probably be a better method than araldite.

 

Ramon the TP twin is basically the same layout as a Stuart 10V but all GM castings

 

Jason

[Cornish JackParticipant @cornishjack]

Ramon and Jason

Thank you for your suggestions – Loctite would seem to be the way to go then.

Jason – my correspondence with Ronnie Baird at Tiny Power indicated that the castings were bronze. Is GM substantially different?

Rgds

Bill

[mgjParticipant @mgj]

Yes, but Loctite can sometimes be a bit iffy on the brasses/bronzes unless one is really good at degreasing, and roughening the sufaces a little. Depends on the load and conditions but its not as good on the rather slippery brasses generally as it is on steel. I take it that we are talking about retainer 603 is it these days?.

 

You’ll also need to be a little careful because the shear strength of Loctite is pretty low. From memory about 1/2 that of soft solder. Its really best for sticking premachined items together, but with care it could well work.

 

The other one is simply to make a plug 1/2 thou oversize, chuck it in the freezer overnight and then press it in or pull it in with a clamp, and then remachine. Ie sleeve. That will get tighter with heat and is unlikely to move anywhere, even under machining loads.

[Jeff DaymanParticipant @jeffdayman43397]

In my opinion a press fit could easily split the trunk if it is only .060-.130 wall as Bill stated. Not a good option in my opinion.

 

I think the epoxy is a good choice to fasten a sleeve in this case, unless Bill knows someone with a TIG welder. In that case, several holes could be cut in the trunk guide and a sleeve welded in with several plug welds.

 

In any case I would recommend that the sleeve be the same material as the trunk guide to minimize the effects of differential expansion.

 

JD

[mgjParticipant @mgj]

Well if its bronze or brass, come to that, why not simply silver solder a plug in and remachine.Machine the plug or sleeve to a decent fit, relieve both ends to allow the silver solder to flow inot the joint, and thats it.

 

Epoxy will be a pain to get in, its very brittle unless you get the rubber loaded stuff, and it always discolours and looks ungrand mostly (if looks are a consideration here) , and it never lasts forever mostly, loctite has limitations, a press fit is more risky.

 

Sort of welding by another route. Pretty painless if one has the torch?

 

 

[JasonBModerator @jasonb]

Bill what they call Bronze in the US can cover quite a wide range of metals and its quite likely close to what we term gun metal. Bronze is probably a little harder than GM depending on the exact alloy.

 

I think the best material will be a piece of continuously cast leaded bronze, you can get this from most of the ME suppliers and its often termed SA660. This is a nice material to work and does not grab or form stringy swarf, it can be bought in hollow section but as your sleeve is probably not much over 3/4″ then solid would be OK. If you do go for loctite then make sure the old bore is cleaned up as it will probably have built up an oxide layer over time.

 

As this part is not going to be stressed then either loctite or soft solder will be the easier options. I would probably go for tinning the two surfaces with soft solder and then sweating them together. This will be more than strong enough to resist the load when the sleeve is finish machined and after that its only a lightly loaded wear surface.

 

Jeff I don’t think you could get down a 1/2″ hole with teh end of a tig to plug weld the liner in place.

 

J

Edited By JasonB on 12/02/2011 15:33:34

[Jeff DaymanParticipant @jeffdayman43397]

Jason as I mentioned I had PLUG welds in mind. These would be done by drilling the trunk guides at 90 deg to the bore in several places, then slipping the sleeve or new bar in, and welding them by TIG from outside. The welds would be in the drilled holes, a fillet weld to the sleeve, then fill the fillet centre with weld. The resulting standing metal over the plug welds can then be filed or ground away flush with the original OD. This method has no access problems as the welding is outside the trunk guide, not down inside a small bore.

 

One alternative I didn’t think of earlier was simply to measure up the original castings and make new trunk guides from solid. I am not familiar with Tiny Power trunk guides, but if they are simple as many trunk guides on other engines are, this would be an easy and economical option.

 

JD

Edited By Jeff Dayman on 12/02/2011 17:39:32

[JasonBModerator @jasonb]

Yes working from the outside would work but not the easiest to clean up given the webs on the A frame.

 

This is the engine, as you can see the trunk guide and A frame are all one so not the easiest to fabricate but could be done at a push.

 

J

[Jeff DaymanParticipant @jeffdayman43397]

Ah – I didn’t realize the trunks had the legs integral with the cylindrical part. You are right, it would be a lot of work to fab them, and not so easy to clean up after TIG plug welds.

 

Well, I go back to the epoxy recommendation then, or soft solder as others have said.

 

JD

[Cornish JackParticipant @cornishjack]

Apologies to all for not acknowledging your most informative suggestions earlier but I hadn’t realised the thread had gone on beyond my last post on the 12th!!

Thank you all but there are more problems (aren’t there always?) to whit – in addition to the standards having been ‘bodge’ bored, they have been bored taper and both top and bottom have been ‘cleaned up’. Result is NO reliable reference surface The tops are different thicknesses, the feet are, similarly, variable and I can’t think of any way I can hold them to rectify matters. If I clamp the feet to a faceplate it won’t be vertical nor would it be if clamped by the top. Trying to shim to verticality would require at least one accurate reference surface and my poor little brain can’t see how it can be done. The exterior is, of course rough casting so doesn’t offer anything useful.

ANY suggestions gratefully received.

Rgds

Bill

[TerrydParticipant @terryd72465]

Hi Bill,

 

A couple of questions before i make what may be stupid suggestions to help.

 

How much of a taper in in the bores, can you measure the top and bottom diameters?

How much is the variation in the thickness of the feet; and

By how much less are the dimensions than the drawings specify?

 

Regards,

 

Terry

[JasonBModerator @jasonb]

Can you clamp the standards to an angle plate fixed to the faceplate, you can then bore true and make your bush a top hat one thus giving some extra metal to the top bolting flange.

 

The feet could also have a couple of bits of flat brass soldered on which would take you back to what is in effect a virgin casting.

 

If the taper is only slight you may be able to fill with solder as you sweat the liner into place.

 

J

[TerrydParticipant @terryd72465]

Jason,

 

You are amazing. You read my mind almost exactly, how did you do that!! The only difference was that I would suggest PB for the base of the feet (I have some thick sheet in small pieces of about 2″ x 4″).

 

I would also have suggested turning a slightly tapered top hat bush, made to fit.. Further, I think silver solder would be the way to go as, if the cylinder has been bored to more or less the correct diameter, albeit off centre, then when the standard is re bored after plugging, the hole will have to cut into the original casting by 0.030″ in order to be central (i.e. about 0.090″+ each side).  In this case I think that adhesives of any sort would be a no no.  Or am I wrong on that?

 

Yours with admiration,

 

Terry

Edited By Terryd on 19/02/2011 16:48:25

[JasonBModerator @jasonb]

I only suggested brass for the feet as they don’t take any wear unlike the trunk guide but really anything in the scrap box would do.

 

Yes if the new bore is likely to cut through the solder or get very close then silver solder would be the best bet, and I would not go with loctite or araldite as I would not want to machine through that, the edges would just tear.

 

J

[Cornish JackParticipant @cornishjack]

Thank you Terry and Jason.

Terry – The rough measurements for the two standards are as follows :-

No 1 -Foot1, LHside 3.7, RHside4.0: Foot 2, 3.6 and 3.8

Diameter at top of trunk guide 17.7 and 17.9 and bottom 17.6

Flange thickness 5.3 one side 5.6 diametrically opposite.

No2 Foot1LH 4.5/4.3, RH4.4/4.5

T guide Diam top 17.9, bottom 17.7

F thickness 5.3/5.6

Plan requires ……%£*!!^£ Imperial!!!

Trunk guide bore approx 17.5!!

Flange thickness approx 2.5

The problem with all these measurements is that they are taken with one anvil on a ROUGH casting surface so not very exact.

Jason, I understand the principle but it’s back to the original problem of not having a reference surface to clamp to.

I have, so far ‘flatted’ the bottom of the feet and the top surface of the flange on some W&D laid on a large mag chuck. Would it make sense to lay some ground flat stock (bar/strip) across the flange and the bottom of the feet and caliper their separation to give some measure of the out of true of the surfaces? Not sure how that would help but the mental processes are not at their best

Rgds

Bill

[Ramon WilsonParticipant @ramonwilson3]

Hi Bill,

Like so many things the first problem is not the only one

 

However, having read your post and the replies heres another view.

 

What do you have as a reference – possibly (hopefully) the turned portion at the top of the standards. Lets take that first and ignore the rest for the time being. Providing that is reasonably true then hold this area in an easily turned bell collet held in the four jaw and set the standard to run reasonably true to the outer diameter of the trunkguide.

 

You should now be able to true the inner to the outside – obviously an unequal cut to begin with so take it easy. Open the bore until it cleans up and run the tool through several times to ensure the least amount of taper. Don’t worry about the size at this stage – repeat for the other standard. Now turn up some ‘brass’ to fit the bores and drill out nearly to finished bore dimension say within a millimeter. Then fit the tube to the bore with whatever you are comfortable with – personally I would still use Loctite but I hear what others are saying and can see the alternatives. For me Loctite cuts out the need to heat anything but “yer pays yer money” etc.

 

You now have a standard with a bore that is reasonably true to the outer surfaces. This can be used to reclaim the top surfaces if required but if they are okay then holding in the collet or this time better still if you have soft jaws hold by the tops again and bore the inner to finish size. You could of course bore this inner dimension to size when turning it as a tube but this way it is in situ. Once you have reached this stage then all else follows – set the standards on an expanding mandrel – again something easily made – and true the feet to the bore (thickness not important) and also the tops. Pads can now be soldered onto the feet and indeed the top if neccessary and remachined to print.

 

If you have not made a bell collet or expanding mandrel before just say and I’ll describe it . The one thing is your parts are not beyond reclamation – yet

 

Hope this helps – Ramon

Edited By Ramon Wilson on 19/02/2011 17:49:19

[Ramon WilsonParticipant @ramonwilson3]

Bill,

Re your last post…

 

I notice you give the top surface of No 1 as tapered across its thickness – 5.3 to 5.6.

Can you tell if this machined face is square to the existing bore ? – given what youv’e described so far I doubt it but if not then this will be the first thing to address. You don’t say if No 2 has the same discrepancy – Ideally this face needs to be square to the OD of the standard to begin remachining.

 

As I see it at this stage, its stilll possible to get a datum but this needs to be checked out first.

 

Ramon

[JasonBModerator @jasonb]

Taking your measurements from the machined faces to the cast faces will never give an exact match, the castings will not be that accurate so 0.1 to 0.3mm is what you have to expect.

 

The builder could only ever get near enough, if the casting was aligned to the trunk guide outer surface its quite likely that the flange and feet would not have been true to this, same if any of the other cast surfaces were taken as datum. Its all about getting the best average. Though the tapered bore is obviously an error.

 

What matters is that the bottom of the feet must be in the same plane as the top of the flange and the bore perpendicular to that, the actual cast surfaces are not important except for visual reasons and I doubt 0.1-0.3mm could easily bee seen.

 

You will have to decide on your own datum to measure from, lets face it you would have to have done that with an unmachined casting anyway. I’d just plug the hole and build up the flange face & feet then start again, if you want to use one of the already machined faces then thats fine just choose the best one.

 

Jason

 

PS Ramon, nice to se your engines in the latest MEB

[Cornish JackParticipant @cornishjack]

Terry, Jason and Ramon, thank you again.

As a dyed-in-the-wool member of the ‘close enough for Government work’ school, there would appear to be a few possibilities there. Re. Ramon’s bell collet, I have checked both castings against the smallest (ID) Myford collet I have and they pull in nicely with about a quarter inch proud of the bottom of the trunk guide. Still wouldn’t give me a universal reference but might be a starting point?

In the middle of cooking a nice looking piece of sirloin at the moment so will tend to the inner man and see what a night’s sleep will produce.

Rgds

Bill

PS Ramon – unfortunately the top of the standards hasn’t been turned on its circumference, only across the width

B

 

[Ramon WilsonParticipant @ramonwilson3]

 

Posted by Cornish Jack on 19/02/2011 19:27:38:

PS Ramon – unfortunately the top of the standards hasn’t been turned on its circumference, only across the width

 

Thats Good News Bill because now you have a ‘way in’

Make up a short expanding mandrel that will go into the bore (about a third of the way due to the taper) from the top end – make it for the largest bore so it can be skimmed to suit the smaller.(It will have to be returned to the 3 Jaw to do that) Any material will do but I normally use steel. This pic should be self explantory the mandrel is expanded with a caphead screw turned to 60 degree to match the centre. The grip exerted by these is considerable – far more than ever needed for the cutting forces involved.

 

Something like this will do.

 

Set this mandrel in the four jaw and get the standard to run reasonably true on the outside as described before with the top nearest the chuck but with sufficient space between to allow a facing cut to true up the top face. Turn the OD of the top at the same time but if you are going to have to build up the top after don’t turn it to finished diameter but  rather leave it .5mm up for a final finishing cut after reclaiming. You now have a good datum face from which to carry out the remaining ops. If you only make this mandrel short due to the taper in the bore I would not be tempted to face those feet at this op but wait until you have the correct bore re- established.

 

Expanding mandrels such as these are an absolute boon IMO as once a bore is done they can be utilised to do so much of the external work relative to that bore

 

Reclaiming mistakes such as you are faced with certainly involes quite a bit of ‘going round the houses’ before getting back to square one but it’s very satisfying to achieve. Hope you are successful in this endeavour as it’s a worthy project. Anything else please shout

 

Regards – Ramon

 

PS Thanks Jason not only for the comment but for introducing me to MEB

 

Edited By Ramon Wilson on 19/02/2011 21:42:29

Edited By Ramon Wilson on 19/02/2011 21:44:00

[Cornish JackParticipant @cornishjack]

Many thanks, Ramon.

Very explicit and (I hope) within my capabilities. I shall give it a try and let you know what results. To paraphrase Capt Oates – I may be gone for a while!! Not the fastest of machinists – by a large country mile.

Again thanks to all

Rgds

Bill

[Ramon WilsonParticipant @ramonwilson3]

Okay Bill,

Good luck – if you need anything else just say or you can always send me a PM.

 

Look forward to seeing your results in due course

 

Regards – Ramon

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