hello Duncan and welcome to the fray! I am not a production engineer - not even a professional engineer - so I can only comment from my own experience in making things, mainly models. However, what you describe reminds me of a large diameter ring gear I once made, but obviously yours has deeper "teeth"! I would have thought a rotary table might do the job, either set vertically or horizontally, or you might consider a gear cutting type of set up with a dividing head and using a slitting saw in place of the profiled gear cutter. Just a few thoughts and no doubt others will have other ideas. You might also consider, if its only a short heat sink, cutting a long bar with fins and then parting off the length you need - save a lot of time I think! Depends whther the housing and finnned unit are one piece or not I suppose, but if not, that might be worth thinking about.

I would also go for a slitting saw and either a rotary table or dividing head, it rather depends on the milling facility you have, saws are available in a variery of sizes and thicknesses, perhaps a quick look at the J and L site would help you to pick one. I am surprised that your existing supplier had trouble in milling these in ali, I do similar parts in steel without trouble so ali should be OK.Iwould lubricte the saw with WD40.

Peter

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Duncan - I would suggest you use a slitting saw on a horizontal type of mill - if you try it on an arbour in a vertical mill and the head isn't spot-on vertical to the bed you might have problems! I used to have a Bridgeport and they are good versatile machines but it was just too big for my needs. So, I would suggest you look for a mill that will give you vertical and traditional horizontal milling capability - but again, I can only speak from my own experience and others may have different views. And if you have a mill with lever operated downfeed on the quill you also have a great drilling machine! I have a slitting saw 4.75 dia by 3/16 thick which you are welcome to borrow for cost of postage but it may be cheaper in the long run to buy one when you get your mill! The other Peter mentioned using WD 40 as a cutting lubricant for aluminium - it is good, but I use white spirit 'cos its cheaper! But thats a Yorkshireman for you!

"Excuse my ignorance but is a dividing head always mounted vertically? I'm assuming it is mainly for cutting gears and indexable? I was wondering how you would keep track of a rotary table, or is this the reason the dividing head exists? "

in answer to that one, they are normally like a lathe headstock and tailstock mounted on the mill table and the better ones are indexable using division plates (again look at RDG to get an idea)

having the saw out of alignment can either break the blade of a thinnish one or lead to a messy end with a thicker one! It is fairly simple to make a device that fits in the vertical head and carries a dial indicator on a radial arm which is a great aid for ensuring proper vertical alignment - not rocket science but a crucial state of affairs. There are many "horizontal" milling machines which have removeable vertical heads. One of the smaller which would handle your need is the Adcock and Shipley 1ES for instance but there are many others. A look on somewhere like http://premiermachinetools.netfirms.com/stocklist.htm will give you some ideas. I have never bought from them but they look good and have a changing range. And they are approachable too, even though they are not in Yorkshire (but not too far away!) Also, have a look on www.lathes.co.uk - an amazing website with details of loads of machines and a "for sale" category too. It will give you an idea of what exists, what is available and an idea of prices.

certainly 2 milling machines would be good - but then you have the job of re-setting up the job when you transfer from one machine to the other. The Americans in the early 19th century got the right idea when they invented interchangeable manufacturing - one machine for one job! But unless you are producing thousands then perhaps overkill and very expensive if you need to carry out several machining operations! Have fun - I'm sure you will.

Hmm,
how about horizontal gangmilling with a number of cutters finishing the cooling fins in one pass?

Cheers
Erik

Having only just seen this posting, and reading the the bottom, I would tend to agree with Erik.

On a vertical miller, set the block to machine vertically on its edge (angle plate, rotary table/dividing head), then having already decided on your fin pitch and width, by adding 'x' amount of slitting saws spaced apart on a single spindle, using a good copious supply of coolant, proceed carefully.

On a horizontal miller, same principle just horizontally.

Hi Duncan-I was away yesterday (picking up the swager)-not a great bargain-but see you've already been getting the usual friendly help this site provides. It struck me after you came round that a bridgeport was probably best for you altho it might have a bigger capacity than you need and a smaller turret miller might be adequate.Chester and Warco amongst others have FE imports of turret millers. I don't have experience of turret millers preferring the" old fashioned" Horizontal and Vertical millers but I think you can set the head of Bridgeorts  over 90 degrees to give effectively a horizontal mill , altho not as rugged as a dedicated Horizontal mill. Gang milling on a horizontal would certainly give the quickest result , milling the whole lot in one pass , although milling doesn't give a top class finish. (this if anything would probably improve the heat transfer characteristics but not the aesthetics)
Incidentally Bridgeport made so many mills that u could almost certainly pick up a s/h Bridgeport probably with DRO or CNC fitted for a lot less than a new FE import-you've just got to inspect whats on offer to make sure you don't get a clapped out one.
You did the right thing pointing out the other swager-it looks about as old as the one I got but not a bad one and in cheaper petrol range.
By the way I've got a lot of horizontal milling cutters (1 Inch bore )not all of which I need and the same with slitting saws when you are next visiting the area. Rgds. Alan

P.S. I think Peter's right about Yorkshire-- the law is an extension of the section specifying the design of a Yorkshireman just under where it specifies short arms and deep pockets .It was part of the more general act of Parliament that famously specified everyone in Liverpool had to have someone in the family who owned a van.