Starting on a casting

[Peter Cook 6Participant @petercook6]

I am about to start machining the castings for the Hemmingway filing machine, and would like to ask advice as to the best way to tackle the job. I have a 250W Sieg SX1LP mill, and a Taig lathe (3.5″ swing), also about 250W. I have machined CI in the past, but only to modify previously machined parts. I have never tackled a raw casting before.

I am comfortable that I can hold the main castings on the mill and will be able to machine them, but am a bit nervous about the ability of the mill to get through the surface layer. I am considering several options and would be grateful for advice from as to which I should use, or for other ideas.

1) Mount the part in the mill and take the surface layer off with a 6mm carbide endmill. 6mm because that is what I have, and I am not sure there would be enough power to take a deep enough cut if I used a 10mm HSS-Co mill although that may be an option.

2) Ditto, but use a fly cutter into which I can put a carbide tipped LH tool. I am unsure if the mill would have enough power to take a deep enough cut to get through the skin.

3) Take the skin off with a coarse belt on the belt sander.

4) Strip the skin off (outside!) with an angle grinder, and then machine the resulting exposed surfaces with the flycutter or endmill using HSS tools.

The castings look as if they have been de-flashed with an angle grinder in the first place, and I think I will have to take the same approach to clean up the edges and sides.

I don’t have an insert face mill – is this an opportunity to spend more money?

Suggestions gratefully received.

[Nigel Graham 2Participant @nigelgraham2]

If you are worried about the mill being able to use a 10mm cutter I don’t think an insert-tool or a fly-cutter would succeed, and if you use an insert-tool as a fly-cutter on this you might end just breaking the insert.

Yo don’t say how deep the milling has to go, beyond the skin; but careful angle-grinding seems a good bet, with care not to go too deep. The linisher is probably safer though possibly slower.

Otherwise use the 6mm carbide cutter. It will just take a lot of winding unless the mill has a power feed!

[JasonBModerator @jasonb]

First question would be does the casting have a particularly hard skin. I have had castings with a hard skin but also had just as many if not more where there was no noticable difference.

I like to fettle my castings before doing any machining so that would be removing any remaining flash, blending in any problems where the two halves of the mould did not quite line up and also a general going over of the cast surfaces to remove any rough or raised areas. This can usually be done with an old file and maybe a Dremel for hard to get at areas and will also give an indication of how hard or otherwise the surface is.

If you have the 6mm carbide then that will allow you to run the mill at it’s fastest speed so it will be giving it’s maximum grunt and if there were any hard spots it is less likely to blunt than an HSS cutter. Don’t go too shallow vertically, try and use a good amount of the side of the cutter but use smaller step over 0.5mm would be a reasonable starting point.

A 40mm 4 insert shell/face mill is an option but use the inserts meant for non ferrous material as they are sharper and will put less strain on the small mill, light cuts maybe 0.3mm deep and again run it at a good surfac espeed which is likely to give a 2000rpm or so spindle speed. Feed at around 300mm/min

A flycutter swinging at a similar radius with a lathe tool and again a **GT insert will cut but the single cutter will not be as kind to the mill as there is a greater “knock” as the tool comes round that you don’t get with a facemill as there is usually always one insert in contact with the work

[Andy StopfordParticipant @andystopford50521]

I built the Hemingway filing machine using an earlier version of your mill and a mini-lathe. The castings are very benign, I didn’t encounter any hard spots, so I should just tidy them up with a file and then use the end mill of your choice – I used the very cheap end mills that come in sets from ebay.

The only part that was challenging for the machines I had was the table – being punched from a piece of black mild steel plate of not much more than the final thickness, it was hard to get a uniform surface finish all the way from the edge to the centre. I soft soldered bits of studding to the back to fix it to the faceplate by the way.

[HOWARDTParticipant @howardt]

It was common for castings to be marked out while in the raw state to ensure enough metal was in the places intended to be machined.  If you take too much metal off the first face you can easily run out of metal on subsequent features.

[Peter Cook 6Participant @petercook6]

Thanks guys. That reassures me and gives me much more detail of the processes I need to go through.

[Alan DonovanParticipant @alandonovan54394]

+1 for HOWARDT comments.

[HOWARDT]

On HOWARDT Said:

It was common for castings to be marked out while in the raw state to ensure enough metal was in the places intended to be machined.  If you take too much metal off the first face you can easily run out of metal on subsequent features.

Watch out for this with the base of the Filing m/c saw bow, you’ve got to make sure enough metal is left to machine the mounting face and have the bores for the top and bottom saw mountings line up and be central. I can’t remember what the instructions say, but I think leaving the bow until everything else is done is the safest approach.

[Peter Cook 6Participant @petercook6]

Thanks again to all for all the helpful comments.

Andy – the bow casting will be done last, but being aluminium the machining issues worry me less, but thanks for the heads up.

[Peter Cook 6Participant @petercook6]

Just to close things and as a final thanks to those who helped boost my confidence. The filing machine is now finally finished – and it works!! This is it set up with a Jewellers 3/0 blade in the saw bow, and some 4″ files in holders on the table.

To face things I used a 10mm HSS end mill with 9mm step over and had no trouble machining the castings, and managed, without too many operator errors, to get all the holes in the right places although I was surprised at how much material I had to remove in places to get to finished dimensions. The bow was no real problem, but turning the table on my little Taig (using riser blocks) was a bit close to the limit  hence the slightly dodgy finish!

It still needs a belt guard and (perhaps) painting but works well for both sawing and filing.

For anyone doing the same thing I finally used a 24v 100w 3000rpm motor geared down 6:1 which gives me speeds from about 70spm to 450 SPM although without the weight of a Myford to hold it still the vibration at the top end is a bit startling.

The only thing that concerned me was the possibility that the lower saw blade adapter could drop down/out if the saw blade broke, and would come into fairly violent contact with the top of the conrod, so I added a grub screw to the bottom block of the bow, and flats on the saw blade adapters – also helps to stop blade rotation when tensioning.

Thanks again for the advice.

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