Stuart S50 (Want to cry)

[Michael Edwards 1Participant @michaeledwards1]

I was giving as a Christmas present last year by my children a Stuart S50 castings kit. Due to health issues I have not been able to get on with the build. I have now managed to start working on the build again.

I have recently purchased a brand new set of ripping milling cutters from RDGTools as I have been fed up with the gold coated ones that I purchased when I got my mill. I have thrown more in the bin than I care to remember.

I started milling the valve steam chest cover last night and to my astonishment I totally wrecked the cutter and the valve steam chest cover. Is this the cutter is the steam chest cover too hard. I have attached some images. The cutter was 12mm.

[Michael Edwards 1Participant @michaeledwards1]

[Norman BillinghamParticipant @normanbillingham91454]

I had the same problem with the steam chest cover on a 10V. Some of the castings Stuart supply are chilled and glass hard. You can return it to Stuarts and they will supply a replacement. If there's enough metal left it's also possible to soften the casting by heating and then cooling slowly – but I'd just get a new one from Stuarts.

Incidentally the "gold" coating is actually vacuum deposited titanium nitride (TiN) and it can be a mark of very good but also very poor cutters

[JasonBModerator @jasonb]

Almost certainly a chilled casting though the photos are a bit small to see clearly.

Stuarts should be able to replace it but not the cutter, BTW mot much point in using ripper/roughing cutters for a job like this as you are buying a cutter which is meant to have it's side used for profiling not just the end for facing.

If you do get a new one then try it with an old file first as it too may be chilled, if the file just skids off it will be. heating to bright red and holding it the re for 10mins then allowing to cool slowly may help or leave in an open fire or wood burner overnight. Carbide tipped tools can help but that would only cover the milling not drilling and tapping.

Final option is to get a bit of 1/8" or 3mm flat steel and mill a decorative recess into that.

Not tried the RDG cutters and doubt I ever will but the ARC ones cope fine with a decent bit of cast iron, notice I'm using the edge not the end.

Edited By JasonB on 12/12/2019 10:26:17

[Anonymous]

I'd agree with Jason that rippa cutters are inappropriate. They're intended for large depth of cut and shallow width of cut, where they reduce cutting forces, not vice versa.

The casting may well be chilled, but a carbide cutter should cope without a problem. They'll cut HSS!

The main issue is a poor quality cutter. The picture of the cutter is a little fuzzy but it looks like all four edges meet in the middle and are not sharply defined. So the cutter will be rubbing rather than cutting. This is what professional 3 and 4 flute centre cutting mills should look like:

On the 4 flute cutter note that only two edges meet, the other two are gashed so they are not centre cutting. The meeting of the edges are crisp and well defined. I'd never buy RDG milling cutters, but I have used the ARC premium mills, and very good they are too. There are two rules for buying cutting tools:

1. Never buy cheap cutting tools

2. See Rule 1

Andrew

[mechman48Participant @mechman48]

Had a similar problem with my S10V, the standard had a chilled surface on the diameter & the only way I had to machine the face was to use a carbide insert face mill & a brazed on carbide tipped tool for the OD…

Bright ring is the chilled iron …

George.

[LambtonParticipant @lambton]

Michael,

Keep on complaining to the supplier, and ask if replacement castings will be soft enough to be machines on small machines using HSS tooling. Get them to test the replacement casting with a file before despatching it.

There are age old reasons why glass hard castings happen. It is usually due to the metal being cooled too quickly which is totally within the control of the casing company. Suppliers of castings for model engineering castings charge very high prices for very small and mostly simple items. They appear to have the familiar police of allowing the customer to do their quality control and simply supply a replacement part and hope the customer will be placated.

Ransoms used to deliberately chill the working face of plough shares in order to give them longer life – a very good reason for produce deliberately hard zones.

Do not accept any excuses such as all casting have hard skins and an initial heavy cut should be take to "get below the skin

Any caster selling you glass hard castings are not doing the job properly.

.

[Michael Edwards 1Participant @michaeledwards1]

Thank you all for your replies. Lesson learnt. Ordering some from Arc.

I tried not to go so cheap on these cutters but I think they were still cheap rubbish

First set were 12 different sizes for £70 (gold coloured end mills)

This new set of rippers £60 for seven (silver)

I tried a gold end mill from RDG first but that did start to rub so went straight for the ripper out of the box.

Just had an email from Stuart Models. They are sending another Steam Chest Cover out. FOC

[DMBParticipant @dmb]

Hi Michael,

Wait for a forecasted dry day and put the lot outside in the bbq and cover with dry sand to ensure a very slow cooling. Cover with scrap sheet steel to keep rain/dew off.

Still use carbide cutters.

HTH

John

[Maurice Cox 1Participant @mauricecox1]

Hi Michael,

I have always put my steam chest covers into a four jaw Chuck, and machined them in the lathe. If you have no chuck backstop to press them against, I flind that pushing the front face of the casting against the face of my drill chuck in the tail stock, or even the face of the tail stock barrel itself, if the casting is suitable size, will get the casting “square” and then the chuck jaws can be tightened.

Maurice

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Edwards 1 on 12/12/2019 14:03:24:

…

I tried not to go so cheap on these cutters but I think they were still cheap rubbish

First set were 12 different sizes for £70 (gold coloured end mills)

This new set of rippers £60 for seven (silver)

I tried a gold end mill from RDG first but that did start to rub so went straight for the ripper out of the box.

Just had an email from Stuart Models. They are sending another Steam Chest Cover out. FOC

First off, chilled cast-iron can be hard enough to give HSS a hard time. Cast-iron is on my list of difficult materials because it's anything between lovely to machine and awful. Usually the hardness is just a skin, but it can go several mm deep and a small casting might be hard throughout. As Carbide has no trouble with hard cast-iron, I always start with a carbide end-mill, only switching to HSS when through the skin.

Secondly,an important part of my learning curve was being told that tools last far longer when made to cut rather than allowed to rub. Rubbing is ruinous because it rapidly blunts the tool without removing metal. And once the edge is blunt, game over – carrying on with a blunt cutter results in poor finish, slow progress, ruined work and bad language. Rubbing is an easy trap to fall into when working with hard materials and a low powered machine. Blunt cutters due to rubbing may be the root cause behind this bad experience.

Ideally, the cutting edge should be forced deep into the material and then moved at a rate that slices steadily through the metal. Small milling machines may struggle and cause the operator to back off and blunt the tool when he should attack. After Andrew Johnson of this forum told me to stop pussy-footing, all my cutting tools suddenly stayed sharp for far longer. To avoid premature loss of edge it's also important to remove swarf and keep HSS cutters cool – flood cooling may be necessary.

Thirdly, £70 for a set of 12 end mills isn't either dirt cheap or very costly. You seem to be buying the same sort of mid-range end-mills as me, and – though I've ruined a few – mine generally give good service. I've not found it necessary to go up-market yet. Just as well, a single 20mm 4-flute end-mill from Cutwel is nearly £40 (not the dearest in the world) and expensive cutters can be blunted by rubbing too…

Glad to hear Stuart have sorted you out with a new casting. Well done them!

Dave

[JasonBModerator @jasonb]

All very well saying force the tool in deep but when Stuarts give you a 1/64th or less machining allowance you don't have much choice.

A really chilled casting can even give carbide inserts a run for their money the good old **GT can come to your aid once again with the "sharper" edge being less likely to be pushed off of the work.

[LainchyParticipant @lainchy]

I had the same with my S50, AND the replacement cover, so beware when it arrives. I totalled 2 HSS cutters, but used carbide in the end… and that was fine. Interestingly, Banggood sells a set of carbide endmills for less than £20, but take a while to arrive.

Hope the rest of the build is going well though I'm still working through mine, but getting closer to the end. I felt exactly the same though when doing the valve chest cover.

Good luck and enjoy.

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Michael,
Welcome to the club !

Although most won’t admit it many a model engineer has been caught out by hard spots in cast iron myself included !

I wouldn’t be too harsh on the cutters you have purchased as they may be perfectly ok for anything except cast iron and I don’t even think twice about using carbide on cast iron – HSS stays in drawer for this material !

I was luck when i built the Stuart score engine a few years back as the only hard spots were on one steam chest cover and only on one corner , a quick rub with an old blunt file picked that straight up and it was marked with a sharpie so i knew what to expect when i started machining it . I think it is good practice to give a chunk of unknown steel a rub with an old file just to ensure it is not hardened before you commit a good cutting tool to it !

[Michael Edwards 1Participant @michaeledwards1]

Thank you all for the replies. Can anyone recommend the cutters they use.

regards

mike

[I.M. OUTAHEREParticipant @i-m-outahere]

And the lid on pandoras box just flung open 😂

A lot of the stuff i use is NOS off ebay – usually Sutton or P&N which are probably not available in the UK .

Ideally i look for HSS with 5% cobalt or M35 .
I can’t recall ever reading a bad word about the cutters from ARC and although I haven’t used one i would be more than happy to buy them based on Jasons recommendations.

If you want industrial grade tooling I’m sure Andrew can point you in the right direction but be prepared to dig deep into your pockets for that grade of tooling !

[lfoggyParticipant @lfoggy]

I have had your experience so many times with cast iron castings that I now only use indexable insert endmills. I have several from Greenwood tools that make short work of chilled cast iron and stay sharp for ages as well.

[JasonBModerator @jasonb]

I'd hold fire and see what the replacement is like with an old file as I suggested earlier.

You can then resurrect that cutter by grinding right across the end at an angle of 2-4 degrees, no need for fancy jigs or cutter grinders and use that on the casing. If it is soft you will be able to cut it OK and you have saved yourself a cutter, if hard you have not risked a new cutter.

Like Foggy for flat surfaces on CI I more often than not opt for insert cutters on the mill which will show what wonders are hiding within, if OK then smaller more detailed work can be done with HSS milling cutters or if a bit dodgy then Carbide ones where the larger insert cutters won't fit such as machining a narrow slot.

[old martParticipant @oldmart]

You don't mention which mill you have, or its spindle fitting. If you cannot use a lathe to face the casting with carbide inserts, then maybe this isn't too big. Much smaller cutters from 10mm diameter are also available with carbide inserts.

**LINK**

[Maurice Cox 1Participant @mauricecox1]

If you are using a mill, why not use a fly cutter? If it is long enough you will do it all in one pass. As to the chilled iron, I had one some time ago, and got round it by giving the casting a brief touch on the side of the grinding wheel; just long enough to remove the rough surface.

Maurice

[JasonBModerator @jasonb]

Just a word of caution following Old Marts link. Do be very wary of the super cheap "face mills" on ebay etc, from personal experience they can leave a lot to be desired – poor fit on arbour leading to eccentric running, poor inserts that will shake you machine to bits and poorly seated inserts. I have posted video of the short comings here before.

Next MEW will have a review of what look to be similar items from ARC but a world of difference in quality for not a lot more cost.

If flycutting a hard casting you will want to use a left hand insert holder otherwise it will take the edge straight off the HSS bit.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 13/12/2019 07:06:08:

[…]

If flycutting a hard casting you will want to use a left hand insert holder otherwise it will take the edge straight off the HSS bit.

.

I am feeling particularly dim-witted this morning, Jason

Could you please explain that advice, in words or in pictures.
… I don’t have much experience of machining of iron castings.

Thanks

MichaelG.

[Michael Edwards 1Participant @michaeledwards1]

Thanks guys.some really good feedback. I will hold off and wait to see what the next cover is like.

The mill I have is a Boxford VM30 with 30International taper (30int takes up a lot of throat space). Looking to make some low profile 30Int adaptors at some point. because if you put in a co-axial indicator or drilling chuck it will only fit if knee is all the way down and the job is low on the table. Even trying to put a spring loaded tap follower in can be a challenge.

[JasonBModerator @jasonb]

Posted by Michael Gilligan on 13/12/2019 08:21:48:

Posted by JasonB on 13/12/2019 07:06:08:

If flycutting a hard casting you will want to use a left hand insert holder otherwise it will take the edge straight off the HSS bit.

.I am feeling particularly dim-witted this morning, Jason

Could you please explain that advice, in words or in pictures.
… I don’t have much experience of machining of iron castings.

Thanks………..

 

Morning Michael, sorry for not getting back to you sooner but I had to pop out to site this morning, hopefully in the mean time you have been able to get a couple more cups of coffee down you to get the brain a bit more active.

1. I'll assume you are familiar with screw cutting

2. If the casting is hard then a HSS flycutter bit will fare no better than the OP's HSS milling cutter probably worse but carbide will hopefully cut the harder material.

3. A left handed holder for the insert or even a left handed brazed carbide tool bit is needed as it presents the insert correctly to the work so that the flycutter can be rotated in the usual direction and keep the edge of the tip more or less tangental to the cut as a line drawn from the top of the tip passes through the ctr of rotation

If you use a right handed holder there are two problems, firstly the tip will not be tangental so you get a negative rake and secondly the cutting force is going against the ends of the grub screws not the solid side of the tool slot.

Hope that has cleared things up for you.

For the other Michael this is a 4 flute cutter that has been given a second life by grinding arross the end as I suggested earlier, in this case I also rounded the leading flute to give me an internal fillet on teh part being machined. Main thin is that slop goes down to a cutting edge, you will have to pick the right one on your ripper that has the lowest full diameter cut.

Edited By JasonB on 13/12/2019 10:30:13

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for that, Jason

(1) and (2) are given

(3) makes sense now

My own [self made] flycuting head looks nothing like yours, so I was struggling to understand the importance of using the ‘left-handed holder’ …

MichaelG.

[Author]

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