Why hold the leadscrew in a 4-jaw chuck ?

Paul.

Could be a complicated answer!

Suppliers like Cutwel, RDG and others will all have a business plan, likely one that allows them to sell efficiently and profitably. Quite often it pays to concentrate on a particular sector: the needs, budgets and techniques used by industrial users are not those of the typical hobbyist. I don't think strong technical conclusions can be drawn from what vendors choose to sell.

Industrial users tend to be focussed on speed; they pay big money for fast accurate resetting, balance good enough to spin cutters at 15000rpm, and effective clamping. At the same time, they are likely to take a professional approach to buying 'fit for purpose' rather than rushing out and buying the most expensive item in the Catalogue. Much more planning than an amateur needs to do.

ER collets are a jolly good thing for both amateur and professional users in that although designed for tool holding, a single collet can also grip work over reasonable clamping distances, usually 1mm. But this is a convenience rather than a universal answer to all work holding problems.

For a job like holding a lead-screw, I guess Robin is after a collet because they have good grip. An industrial user turning many lead-screws might solve the problem by buying a collet of the right size (not ER – it would be some other system), or by making a soft-collet, or by specifying a purpose built clamp. But for a one off, I think most workshops would go for a 4-jaw chuck as Paul suggests. A 4-jaw will grip as effectively as a collet; the only disadvantage is the time taken centring them, especially if you've not done it before! For a job like this, I would only use a collet if I happened to have one of the right size already, otherwise I'd get the 4-jaw out.

Differences between home workshop and industrial techniques are worth looking at I think. In Mal Webber's Howitzer thread Niloch posted a link to a silent film showing how 8" shells were made in Canada circa 1917. It's useful viewing for the variety of production techniques used a century ago and comparing them with how a hobbyist might approach the same jobs. In the film work holding isn't done with conventional chucks or collets; rather – in the interest of speed and accuracy – arbours or special to purpose chuck/clamps, some pneumatic are used. Mostly the work is done with lathes, but not general purpose machines of 'our' type. Instead they are customised to do one job efficiently. There's a nice sequence showing parting off in a 'lathe' pulling front and rear cutters together under power; not a standard cross-slide, and pretty useless unless you have a lot of 8" parting to do!

My point is there are a series of borders and overlaps between hobby machining, jobbing workshop practice, production, and mass production. The best tool depends on who you are and what you're doing; not on 'quality', or 'industrial best practice'. There's a lot to be said for hobbyists buying from hobby suppliers and preferring hobby techniques.

Dave

I bought 29 and 30 some time ago and recently picked up 30, 31 and 32, all of them are marked with the standard 1mm compression range and work fine that way.

Message sent, Maurice

MichaelG.

You beat me to it Howard. An aluminium bush bored and split in the 3 jaw would be an inexpensive but accurate way to hold the lead screw.

Hi,

It might be worth contacting this precision engineering company to ask for advice and get a price on an oversized collet? : **LINK**

Zane