How on earth do you mill a curve? (machinist question)

[northwind]

I've got myself a lathe/mill combo (well, to be more precise it's a Unimat SL, so it's really a 1/3rd scale lathe/mill combo, just about big enough to sharpen a pencil... but what a lovely wee toy) and I've been mucking about with it. Turning's simple enough, and I've done a few bits of reasonably succesful milling with a small end mill, but I can't get my head around how to machine out a curve.

I want to make myself some aluminium brackets with curved ends y'see. Trying to do it with the table always gives a horrible wobbly line at best, but that could be down to be being completely rubbish... CNC is obviously out of the question, though it's been done with stepper motors it doesn't make any sense given the quality of the hardware. So, how is it done? I've thought maybe move the work not the tool, but I can't see any easy way to do that. I can see some ways of making something that'd maybe work, as long as there's a hole in the middle of the piece...

[Spanner Man]

Good morning.

You need a rotating milling table, these are some available that are not too expensive but you will rarely use it.
If I were you I would mark out the work & mill the curve as close as you dare, & then finish by hand using a file.

I have a 4.5 inch Boxford lathe, which although constructed to toolroom standards does show it's limitations when doing anything other than normal turning i.e. turning tapers or thread cutting.
Machines such as yours which are intended for hobby use tend to be very time consuming particularly when milling. So often one has to 'cheat' when it comes to machining a radius if extreme accuracy isn't required.

For a good range of affordable machine tools & accessories try www.rdgtools.co.uk. They will probably have anything you require.

I must warn you that machining is addictive, & it's easy to get carried away & spend a small fortune on things you will never use

Cheers.

Like the man says,for the cost the extra kit it would probably be cheaper several times over to get the whole job done by a local engineering firm. An alternative Andy is wait till a local firm is closing down or see if there are any auctions for engineering kit i.e ex MOD stuff is good

Rotary milling table as mentioned,(aaw such sweet memories of my apprentice years!) Another method although a bit drawn out, is to mark the metal to be cut with the desired curve profile and niblbe away at it with cutters taking off a series of "flats" gradually as the flats merge in to each other the finishing curve can be tidied up by filing or grinding.HTH.


(What's he building now?????)

Originally Posted by Pedrosa

(What's he building now?????)

In this weather?


A roof

Nah, he's replaced everything else on the SV.


The time is now to do his version of a Vyrus milled alloy frame.
I expect to see this unveiled for the Ice Cream Run!

Or go to a college machinery evening, where you allow to make full use of the workshop. My college currently does this.

At first glance at the thread title i thought you were hacking down a curvy to make one of them horrible pointy jobbies

Originally Posted by Spanner Man

If I were you I would mark out the work & mill the curve as close as you dare, & then finish by hand using a file.

What he said. That's the way I used to do it (when I had access to a mill).

[timwilky]

I really miss having access to workshop facilities. When I worked for Leyland I had the benefits of a whole prototype department geared up for building trucks/engines/gearboxes etc. So special tooling, gear cutting, access to metallurgist for advice on materials, and a huge source in the material stores, heat treatment and plating. Oh happy days.

Then when I started with GEC similar facilities available but simply huge. Set up for
machining turbines and generators so 40ft between centres, vertical borers that can turn 30ft diameters etc. There the welders were top class.

Now, I only have access to my garage, bench grinder and a file are the limits of my metal shaping. My local colleges offer nothing. I keep looking out for a decent lathe and milling machine but I cannot justify the space/cost. Anyone want to give me a boxford or colchester type centre lathe with metric and imperial screw cutting and a cnc milling machine.