Member postings for IanH

I have "1 thou per inch dia" in my head from somewhere as a "general engineering" interference fit.

I come across interference fits mainly in two applications - One is for pressed up cranks in engines (mainly JAP V twins), here the interference typically used is 4 thou, some folk push this up to 5 thou, this is on shafts of around 1 1/2" diameter depending on the application. The shafts are case hardened and ground, the crank discs are surface hardened - tuftriding for example. The hole in the crank needs a bit of a lead and the shaft needs a bit of a radius - they are almost always pressed together cold with lubrication (Castrol R seems popular) . Failure to surface harden the crank leads to the shaft broaching it's way through with the loss of the interference fit.

The other application is the fitting of valve seat inserts in cylinder heads. Interference fits here vary, Serdi (manufacturer of valve seats and associated tooling) seem to use 6 thou interference. Their tooling system aims to give the 6 thou interference by design. It is not uncommon then to see people hammer the valve seat into place (see YouTube) . The standard Serdi valve seats have a generous nose radius to help them in and a mandrel to guide them is also used, fitting into the valve guide. People working on our pre war JAPs tend to ease off on the interference fit, down to 3 thou or maybe 4. Valve seats falling out can be a problem, but there are various factors in play here.

I have been experimenting fitting valve seats in a pre war head and used the Serdi 6 thou interference, but used temperature difference to fit them - I am not a fan of the lump hammer. The CI head went into the oven at top wack, then the local AI man came around with his liquid nitrogen to cool the seat down. With that delta t the seats dropped in, only a light tap with the hammer was used to make sure the insert was properly seated. The old CI head survived the heavy interference without cracking.

Ian

I get involved mostly with JAP V twins on Morgan Three Wheelers and one or two other odd balls, and more recently JAP 500 singles. Safe valve guide clearances for these engines are considered to be 2 thou on the inlet and 4 thou on the exhaust. Some practitioners opt for 2 thou all round, and some get away with it.

Valve guide material was Meehanite, although Colsibro is currently offered as an alternative. Valve guide lubrication is a bit hit and miss - there are drillings through the head into the valve guide and small pipes feed oil from a collector on the back face of the rocker box into these. Lining up the hole in the head with the hole in the guide is important. The rocker box may or may not be positively fed with oil. The worst case is no positive feed (like my engine), oil “mist” is thought to find its way up the pushrod tubes from the timing chest which communicates with the crank case, into the rocker box, some then finds its way to the valve guides. I add a bit of oil to the the exhaust valve guide each morning before setting off but the rocker box is always wet inside.

The little cap on top of the valve stem we know as lash caps. These are currently being machined from EN24T rather than EN36 hardened.

Measuring valve guide bores reliably can be tricky enough, but parallelism is critical. One engine that we dealt with recently that nipped up when working hard was found to have plenty of valve guide clearance at the ends but the middle of the valve guide was tight - the bore was barrel shaped. I think also that adjusting valve guide bores can be a game for any number of players....reamers like to have a bit of work to do and taking an extra thou out with a used reamer, especially in the bronze like materials, may not work. Adjustable reamers don’t always behave either.

Ian

Nigel,

Bearing in mind that when I listen to the radio in the workshop I can miss odd chunks when I do something noisy....Ben responded to the Liberian, Joel I think, and asked how he could help. Joel described his plan but Ben proposed an alternative, his suggestion was that if Joel sent through some good photographs of Liberia, he could get them published, and was prepared to share the proceeds 50/50. I should say that Ben is no mug and is sharing his experience with his social media followers.

Joel sends some poor photos, so Ben sets about coaching him in photography and even sends him a low cost digital camera to help. Joel works diligently at improving his skills and ends up sending good quality to photos to Ben. Ben realises that he has to follow through with his promise to monetise the photos or else become the scammer himself, so he publishes a book of photos. As promised, he sends 50% of the proceeds to Joel.

Ben then decides that he would like to send his share of the proceeds to a charity in Liberia and asks Joel for a recommendation. Joel recommends a local school, but rather than give the contact details, he asks Ben to send the money to him to pass on. Now comes the leap of trust.

Ben trusts Joel and sends the money.

The money gets to the school where it makes a real difference. Ben later visits Liberia and he and Joel become firm friends......or something like that.

Yesterday, whilst I was busy in the workshop, the BBC Radio 4 program “Sideways” came on. This was episode 39 entitled “Please, I beg you”. It is described as follows;

When Ben Taylor receives a Facebook message from a stranger in Liberia, asking in badly spelled English for financial or business assistance, he quickly assumes it’s a scam. But instead of just ignoring the message, he decides to find out about the person behind it. In this episode, Matthew Syed explores what happens when you let your guard down and make a leap of trust.

It is as least an interesting listen and made me think.

Ian

I have pm'd you Rod regarding a shared purchase.

Ian

Edited By IanH on 07/01/2023 12:14:58

Well, apart from a minor mishap on opening day in 1896 when an apparently overloaded loco lost control on the way down, and having been abandoned by its crew, fell off the mountain! The coaches stayed on the track only to be hit by a following loco.... **LINK**

....the railway seems to have an excellent safety record, so we must assume the team up there know what they are doing.

It does look like the relatively soft rack is allowed to wear away protecting the hardened pinions on the locos which must be expensive and tricky to replace.

This is a photo of some bits of rack lying at the side of the track around half way down. I imagine they have a specification indicating how much wear can be tolerated before replacement, and an inspection regime to check the condition of the rack through the operating season.

Walked up Snowdon (Yr Wyddfa) today with a couple of pals. Fabulous walk and lovely weather.

Coming up the Pyg Track we came to the Snowdon Mountain Railway track and I was astonished to see the wear on the rack. Whether this is one season's worth or more I don't know. There was a gang out lower down the mountain working on the track and I assume/hope they were replacing the rack.

I thought folks might be interested to see the extent of the wear.

Another thought.....if you were on a ship or in a space station orbiting the Earth you could still make things despite not being able to level your machines, so not essential. But whilst you are on the Earth it seems a pity to waste gravity 😃

Well I would say yes, but only because I sometimes use “gravity” as a handy reference for some set ups. When I am not going for a very high level of precision, it is handy to use one of those electronic level gizmos on the work to indicate that you are more or less horizontal or vertical or at any desired angle.

I am also working on some tooling for cutting valve seats where I am going to use a circular spirit level located in the valve guide to indicate that the valve guide bore is vertical - if the mill is also properly levelled, I can assume that the valve guide is then aligned with the mill vertical axis......more or less.

If you set everything up from the table i.e. the mill only references itself, then it doesn’t matter.

Ian

Hi Dave,

Very sorry to hear about your Dad. I am also in the village so give me a shout if I can help things along.

Ian

How about a Centec mill? My first milling machine was a Centec and I thought it was excellent - vertical and horizontal milling in one compact unit.

One of these is going to pop up in a week or two following the sad loss of a local model engineer. I will have more info and some photos in a week or two if you can hang on.

Ian

My last lot cost between £3 and £10 each depending on the size of the cutter. Vat on top I guess.

Ian

Raynor Toolservices in Market Drayton raynortoos.co.uk - about once a year I send them a mixed bag of milling cutters with instructions to grind to the next imperial size down and they come back individually boxed up and labelled having been CNC ground.

Hi,

I recently acquired a pair of Delapena external hones, one small and one large. Some of the stones are in poor shape and I would like to sort them out.

I understand that these tools are no longer made so I am looking for replacement abrasive stones assuming I can remove the existing stones from the holders and glue in replacements.

The stones are numbered 11 to 15-P8-F for the bigger tool and 3 to 6-P8-F for the smaller one. Looking at the Delapena Web site I think F denotes silicon carbide but I can't see anything to decode grit size.

The hones will be used on decent steels, En16, EN24 and case hardened EN36B for example.

The bigger stones are 2" long 3/16" wide and 1/8" thick, the smaller ones are 3/4" long by 0.1" Square.

The existing holders could be modified to suit stones of a different section assuming I can cut the replacement stones to length somehow.

I have emailed Delapena to see if they have any info or suitable stones, but I thought I would ask the forum at the same time as someone is bound to have done this already or will have some good ideas.

Thanks,

Ian

Give these guys a call **LINK** they cut some spring steel steering wheel spokes for me some time ago.

ian

Here is the tool holder finished (probably). It is a bit like a boring head but cruder in that it is set to a gauge rather than having a micrometer screw, also it needs to show a concentric bore on the bottom at all times to allow a pilot to be mounted which locates in the valve guide, hence the horseshoe shape.

The pocket for the insert was machined on the CNC machine. I glued the insert in as suggested, then clocked up the hole in the tool. I moved 3 thou toward the back of the tool holder, and drilled and tapped M3. The result was terrible for some reason and I ended up soft soldering some shims in the pocket to sort it out. Not sure why it went wrong, I suspect the tapping size hole drilling was not stiff enough somehow..... I will try harder next time.

Ian

Thanks for these answers, very reassuring to hear. The mounting screw is M3 so it looks like 3 thou offset toward the shoulders should do it.

Thanks again,

Ian

I am working on a tool holder to mount commercially available inserts to machine multi angle valve seats.

I have made the basic tool holder based around standard Serdi pattern tooling, but have not yet decided on the specific insert type. The two options I am considering will both have a pocket with two shoulders for the insert to locate against. In both cases the inserts are held in with a standard looking countersunk torx screw through the insert

My question is to do with the location of the tapped hole for the screw. I have the impression, based on some of my existing commercial tooling, that the position of the screw may be biased a little toward the shoulders rather than being truly Concentric with the hole in the insert. Nipping the screw up gives the impression of the countersunk part of the screw going home and jamming the insert into the holder.

The question then is, should the screw be biased toward the shoulders or not, and if so, by how much?

Ian

My Bridgeport came in to my back garden workshop over the house with the help of a 35 Ton crane. The crane operators were fantastic, putting the machine down at the workshop door with tremendous precision.