Milling, lathing .. or what?

[bricol]

Slightly worried by the people in this thread saying surface grinder for heads.... proper engineering books will usually say that you want a surface roughness for head gasket (especially MLS gaskets) and surface grinding is far too smooth.
Plus you wouldn't surface grind a modern aluminium head... would you? Genuine question.... I didn't think it was possible without loading up and clogging regular wheels.

One local machine shop has a big Chen Ho set up with a fly cutter permanently - just for skimming engine parts as they come in. Usually takes him 30 mins start-finish and it's an easy £40-£50 for him...

Exactly.

Its not exactly rocket science either - setup, drive machine - even I managed it with an old Mostana mill after hours with a cutter not wide wide enough to do it in one pass.

I wouldn't try it on my hobby mill - which I think the OP has already realised.

 

[bricol]

For instance, it may not be absolutely desirable in terms of rigidity and thus flatness and paralellism to lop a few hundred microns from the top of a cylinder head using a turret mill. However, it's a heck of a lot more desirable than rubbing the thing back and forth on a glass plate topped with sandpaper.

Although I managed to reduce the deck height on a K-series block sufficiently well using a large lump of flat aluminium and emery cloth, basically draw-filing across the top, to get it flat enough, true enough and with the correct amount of liner protrusion for it to reliably develop 200bhp - quite good fun in a half tonne car

 

[minimutly]

Using a 4 inch flycutter on a table top or turret mill to skim a head without steps, concave or taper is a sure way to drive yourself nuts, but if that's all you got....

 

[Munkul]

Why not? I did.

Fair enough, but what sort of heads?

 

[conor1n]

Thanks guys, very interesting debate here.

I guess I won't be doing heads, based on my lack of skills experience, which is fine by me. I'm just trying to gauge what is possible at this stage.

I do see from some skimming on YouTube that it is very technical for precision work.

....and yes, the mig-welding curse is alive and well here. But as one man said the other day, you could be spending your money on A LOT worse.

 

[Maker]

I bought a mill before a lathe, thinking square and flat things were more useful than round. I couldn't use it until I had the lathe as I needed to bore out a pulley to use it.

I still very rarely use it, mostly as I don't have a lot of tooling for it, but it's not that often I need it, whereas the lathe seems to get used for every single project, however small.

 

[ukracer]

Why not? I did.

There will always be lucky exceptions (Or extremely talented ones. But in general....

 

[Munkul]

Personally, I don’t buy the ‘too flat, too smooth” claim. The cylinder head clamps vertically against the gasket. As I see it, all it needs for a good seal is a flat head and deck. It is not sliding anywhere when tightened down, and it is the fire rings that provide the seal for the highest pressures.

I suspect that comment is derived from some source that wants to justify their machinery.

Have you ever seen a head that repeatedly burns up HGs? I have. 6 thou out-of-flat. Not very much.

Old fashioned engines with thick composite gaskets are a lot more tolerant of out-of-flat heads than modern alloy heads with MLS gaskets. There is VERY little give or room for tolerance with MLS gaskets.

It's a lot cheaper to pay an extra £40 for a head skim than it is to have to pull a head for a 2nd time after a premature failure.

 

[conor1n]

It's a lot cheaper to pay an extra £40 for a head skim than it is to have to pull a head for a 2nd time after a premature failure.

So this is one of the reasons, I don't think i'll ever be getting into (unsupervised) engine work.. too much effort if things go wrong.

 

[Mr Fro]

Fair enough, but what sort of heads?

Just bike heads.

 

[addjunkie]

It's a lot cheaper to pay an extra £40 for a head skim than it is to have to pull a head for a 2nd time after a premature failure.

Where is this place thatll skim a head for 40 quid, I need to know just in case I need something done.

When stuff is made by machining the surface finish is normally specified on the drawings. Quite often for sealing faces a record finish is adequate. Bare metal to metal is a bit different.

As for a hobby mill, if its big enough to get a head in and do it in one pass Id give it a go. Worst case scenario Id need a new one. Or something big enough to scrape/ lap it too.

 

[minimutly]

Oh no, don't lets get into bluing and scraping, that way lies endless days of frustration....or enjoyment, depending on your mental state?

 

[stevethegrease]

As for machining cylinder heads.... Alloy heads off petrol engined cars are nearly as soft as soap and a doddle to machine with pretty much whatever method you want to use.
That said Indirect injection diesel heads have precombustion chambers shrunk fit into the head ( also called possets I believe) these are rock hard in contrast to the soft alloy of the head. I have seen heads like these scrapped by machining with a fly cutter. The fly cutter* is fine on the alloy, but bends out of the way when attempting to cut the hard precombustion chamber, and then springs back after clearing the insert leaving huge chatter marks and a dreadful surface finish that no gasket would ever seal. Heads like these, I believe are better finished with a type of grinder, not a regular surface grinder where the axis of the wheel is parallel to the surface being machines but where the axis of the wheel is perpendicular to the face being machined. Being ground the wheel copes with the different materials , but cuts across the face and at 90^ to it rather than along it, leaving a mating face for the gasket rather than the almost mirror finish of a J&S surface grinder.

Bo$$ocks to scraping, it's hard work.

* dependant of course on speeds , feeds, the type of cutter and the material of the hardened inserts

 

[Barking Mat]

As for machining cylinder heads.... Alloy heads off petrol engined cars are nearly as soft as soap and a doddle to machine with pretty much whatever method you want to use.
That said Indirect injection diesel heads have precombustion chambers shrunk fit into the head ( also called possets I believe) these are rock hard in contrast to the soft alloy of the head. I have seen heads like these scrapped by machining with a fly cutter. The fly cutter* is fine on the alloy, but bends out of the way when attempting to cut the hard precombustion chamber, and then springs back after clearing the insert leaving huge chatter marks and a dreadful surface finish that no gasket would ever seal. Heads like these, I believe are better finished with a type of grinder, not a regular surface grinder where the axis of the wheel is parallel to the surface being machines but where the axis of the wheel is perpendicular to the face being machined. Being ground the wheel copes with the different materials , but cuts across the face and at 90^ to it rather than along it, leaving a mating face for the gasket rather than the almost mirror finish of a J&S surface grinder.

Bo$$ocks to scraping, it's hard work.

* dependant of course on speeds , feeds, the type of cutter and the material of the hardened inserts.

Interesting.

The company I used to use for skimming heads wouldn't touch alu heads.

My neighbour has for a couple of years has a surface grinder, he does my occasional head now.

He lost a series of head gaskets on a race day.

As he said, what I've learnt about Rugosity in the last six months, I could have written a book.

I had to Google it:

Rugosity, fr, is a measure of small-scale variations of amplitude in the height of a surface,

{\displaystyle f_{\text{r}}=A_{\text{r}}/A_{\text{g}}}

where Ar is the real (true, actual) surface area and Ag is the geometric surface area.[1]

Rugosity calculations are commonly used in materials science to characterize surfaces, amongst others, in marine science to characterize seafloor habitats. A common technique to measure seafloor rugosity is Risk's chain-and-tape method[2] but with the advent of underwater photography less invasive quantitative methods have been developed. Some examples include measuring small-scale seafloor bottom roughness from microtopographic laser scanning (Du Preez and Tunnicliffe 2012),[3] and deriving multi-scale measures of rugosity, slope and aspect from benthic stereo image reconstructions (Friedman et al. 2012).[4]

In short, a surface grinder can make a cylinder head too flat.

I think...

 

[Munkul]

Where is this place thatll skim a head for 40 quid, I need to know just in case I need something done.

PMed

 

[bricol]

Slightly worried by the people in this thread saying surface grinder for heads.... proper engineering books will usually say that you want a surface roughness for head gasket (especially MLS gaskets) and surface grinding is far too smooth.

Please actually quote a couple of tomes and I might then have a search for myself, or serk advice from another forum.

BTW, one would select an appropriate grinding wheel for Aluminium. I’ve only ground a CI block deck and a CI cylinder head so far. Dead flat from end to end, side to side and corner to corner.

Your earlier post ‘sort of‘ claimed texts as saying the metal is too smooth. Please provide the evidence.

The gasket maker will specify the surface finish required - 60-80 Ra for cast iron and 50-60 Ra for aluminium seems common. Both easily achievable with a mill. As they are with grinding too of course - but a grinder, given the right wheel and set-up, can easily go way too smooth - easily into 4-8 Ra - and that will not give the "grip" required.

 

[bricol]

Where is this place thatll skim a head for 40 quid, I need to know just in case I need something done.

When stuff is made by machining the surface finish is normally specified on the drawings. Quite often for sealing faces a record finish is adequate. Bare metal to metal is a bit different.

As for a hobby mill, if its big enough to get a head in and do it in one pass Id give it a go. Worst case scenario Id need a new one. Or something big enough to scrape/ lap it too.

The most horrendous looking place in Keighley will do a 4cyl head skim for 30-40 quid. I know how to get there, but not its address or details. Done while you wait and make small torque, sorry, talk.

 

[Munkul]

Have you ever seen a head that repeatedly burns up HGs? I have. 6 thou out-of-flat. Not very much.

Pray tell me how a surface-ground head is going to finish up 6 thou out of flat. I’ve seen engines that have blown a head gasket more than once. Usually down to the person who didn’t check the first time the gasket blew. 6 thou out-of-flat is a huge amount for a cylinder head. 2 thou is often the limit - and I would prefer less, but it would depend on the engine size, I suppose (but those large heads would not fit either my mill or surface grinder, anyway).

Here is what you posted previously, before shouting about non-flat heads:

Slightly worried by the people in this thread saying surface grinder for heads.... proper engineering books will usually say that you want a surface roughness for head gasket (especially MLS gaskets) and surface grinding is far too smooth.

Please actually quote a couple of tomes and I might then have a search for myself, or serk advice from another forum.

BTW, one would select an appropriate grinding wheel for Aluminium. I’ve only ground a CI block deck and a CI cylinder head so far. Dead flat from end to end, side to side and corner to corner.

Your earlier post ‘sort of‘ claimed texts as saying the metal is too smooth. Please provide the evidence.

I don't have to prove anything, you just have to google it. Cometic, cosworth etc. Will give a Ra value you'll never hit with a surface grinder.
I mis understood your post before though, i thought you were saying you didn't see the point in skimming a head at all, sorry, my mistake.

 

[minimutly]

As for machining cylinder heads.... Alloy heads off petrol engined cars are nearly as soft as soap and a doddle to machine with pretty much whatever method you want to use.
That said Indirect injection diesel heads have precombustion chambers shrunk fit into the head ( also called possets I believe) these are rock hard in contrast to the soft alloy of the head. I have seen heads like these scrapped by machining with a fly cutter. The fly cutter* is fine on the alloy, but bends out of the way when attempting to cut the hard precombustion chamber, and then springs back after clearing the insert leaving huge chatter marks and a dreadful surface finish that no gasket would ever seal. Heads like these, I believe are better finished with a type of grinder, not a regular surface grinder where the axis of the wheel is parallel to the surface being machines but where the axis of the wheel is perpendicular to the face being machined. Being ground the wheel copes with the different materials , but cuts across the face and at 90^ to it rather than along it, leaving a mating face for the gasket rather than the almost mirror finish of a J&S surface grinder.

Bo$$ocks to scraping, it's hard work.

* dependant of course on speeds , feeds, the type of cutter and the material of the hardened inserts

this I agree with - I never flycut an alu head that has steel inserts, no way. You need to grind them with a wet stone.
Edit to add my thoughts on Ra - some roughness is to be desired, to aid “sticking” of the gasket - specifically the fire ring, which could be subject to early onset, or even severe detonation. Yes, it’s not a fix, but why engineer in a weak spot?

 

[jim noonan]

So guys,

I've recently been looking into milling. Mainly because it's cool.

I've been wondering about getting a mill. Just to make stuff. I would rather a mill versus a lathe so I can make non cylindrical parts.

Would it be fair to say that milling is a whole vocation all on it's own.. Especially the manual (non CNC) type where there is a lot of skill required.

Is it the kind of thing that is not worth getting into unless you plan on spending a lot of time learning and practicing? Also, what are the Warco £1000-2000 machines like, can you do much with them?

Would it also be fair to say that the mill itself is only the start. You could easily find yourself spending the same again on things like a DRO and various attachments etc, before it is of much utiinglity?

I'm not even sure I know what I can or want to make, just that they are cool, and making stuff is cool.

Thanks

I'm really interested in your question. I have a very small, very old lathe which I am looking to replace. I have spent hours and hours researching the relative benefits of different lathes and, like you have become intrigued by the possibility of a mill. I am not an expert machinist but I think I can make one very definite assertion as follows: If you do not have a specific purpose in the sense of making a particular product or undertaking a specific set of machining tasks it is highly unlikely that you will find a mill more beneficial than a lathe. It's a real cliche but the lathe is vastly more versatile than the mill. With creativity and imagination a lathe will produce flat surfaces but a mill is less able to produce round items. Take a look at blondihacks on youtube about essential metalworking workshop equipment. She gives a really well informed and experience based reasoning for what you might want in a small workshop. Also, please look at lathes.uk for the most thorough information on any or all machines and an amazingly detailed account of their specs and history. RE Warco, my view is that they were originally part of the "chinesium" influx but that they have continued to scrutinise and improve their products over the years and are now a reliable supplier (with the benefits of purchasing in the uk) and I am intending to buy a Warco lathe when my pension comes in! If I can get one with a milling head i will probably do so but their are issues with stiffness on combined lathes / mills. There was an immaculate chester lathe / mill on lathes uk a few months ago for a ridiculously low price.
A good lathe, unless you need a mill for specific purpose is almost inevitably going to be more versatile than a mill. You know the Cliche "the lathe is the only instrument that can replicate itself". It's rubbish actually, in the sense that the lathe cannot cast its bed or ways etc. but it does reflect its massive versatility. Just my thoughts
Good luck
jim