Questions questions

gasman · 18 Sep 2015

Forgive me for ignorance for I am new to this metalworking business but I have questions about using a lather
First, why do they come with tapered fittings e.g. MT2 etc doesn't that just mean it is possible for the 'joint' to come apart when you don't want it to?
Second, why do you need to have collets in all the different sizes for a mill? Why not have the collet the same size and vary the cutting bits like a router does - just seems that you end up duplicating everything??
Sorry if these are obvious but I don't really 'get it' yet!
Regards
Mark

AndyT · 19 Sep 2015

Tapered fittings have the really important virtue of automatically giving you proper concentric alignment. Other options would need fiddly adjustment each time to get them centred. They are also cheap and simple to make.

Although it seems odd, the fit between two steel tapers made to the right standard of accuracy is amazingly strong and the connection doesn't come apart in use. To break the connection you need to use something to push it apart, either a central threaded ram or a simple bar and hammer combo. You can't just pull the taper connection apart by hand.

One other virtue is that the Morse taper standard is so old and so well established. I can buy new fittings for my antique Barnes lathe with no problems at all.

Harbo · 19 Sep 2015

Collets are also used for holding round sections of materials which come in all sorts of diameters.

Rod

woodpig · 19 Sep 2015

In metal working rigidity is very important so a 5/8" end mill needs a 5/8" shaft. You could use a 5/8" shaft on a 1/4" cutter but it's a waste of steel.

CHJ · 19 Sep 2015

AS Harbo says, the prime function of a collet system for a lathe or work holding tooling is to hold round section stock as accurately centred as possible whilst machining it without having to resort to adjusting for true 'running'

The reciprocal of this are Collets intended for heavy cutting tool use on a milling machine and are of a more limited bore range and invariably having a thread or other locking system associated with the design to prevent rotational slipping and tool pulling out of fixing under loads, Look up Clarkson Cutters for instance.