Jig borer

Hopefully a simple question....

What's the difference between a jig borer & a milling machine? As far as I can tell, jig borers seem to have an integral rotary table but apart from that?

Or is the clue in the word 'borer'?

Brian

The other clue is in the word 'jig' ... not in the sense of dancing, but in the sense of a 'template' for making things.

Decent article on Wikipedia: **LINK**

https://en.m.wikipedia.org/wiki/Jig_borer

MichaelG.

Borer is indeed the clue. Jig borers are designed to accurately position holes, whether drilled or bored, in the workpiece. Mills are desined to cut into the sides of workpieces as well as make holes.

Jig borer table screws are intended to shift the tables precisely to the desired position on the sideways. The need for precision over along working life means both are of comparable dimensions to milling machine equivalents so pretty much any jig borer is capable of being a vertical mill. Main limitations will be in the spindle and its carrier which are primarily designed to take vertical thrust. Sideways strength being more to ensure stability and accuracy rather than taking cutting loads. Putting a large cutter in will ruin the spindle for jig boring jobs in short order but even Moore admit that small cutters and cuts are OK. In industrial practice using an expensive jig boring machine as a light duty miller is just plain daft. In home shop use a pensioned off jig borer will still be a more than decently accurate mill. home shop folk don't use machines as heavily or as industrial folk so the difference can be moot. Proper jig borers are big tho'. Little different for smaller machines such as the bench top Downham/LInley, the BCA and other "improved Wolf-Jan" breeds et al. Scale effects mean that overall they are much closer to a conventional small mill in design and construction so can be very much dual purpose. But small cutters only. The sliding head spindle support is inevitably far less robust than a proper mill layout with the spindle in the main casting.

Clive.

As Clive said. A jig borer will have accurate table positioning, within 0.005mm/0.0002" is a manageable tolerance. The spindle will also be accurate in runout and z-axis, so precision bores can be produced using single point cutting as against a drill/ream hole. Machines are heavy compared to a mill of the same envelope and may use glass scales. To maintain accuracy the machine should be within a temperature controlled room.

Thanks one & all....

The reason I ask is that I've seen a Sigma Jones Jig Borer for sale at what sounds like a reasonable price and wondered if it would be a good addition to my man-cave for light milling.

Brian

.

It's probably the same general style as my BCA

Have a look at these pages: **LINK**

http://www.lathes.co.uk/bca/

MichaelG.

Brian

The Sigma-Jones, like the BCA and the similar machines, is a bit of an odd duck. Its not really a jig borer more an instrument makers light mill. Of necessity, given the class of work it was made for, it was built to the sort of accuracy associated with proper jig borers. It will work fine with small milling cutters but unless you do the right sort of work the thing is an unmitigated pain in the butt to use. I was very happy to swop my Ultra version for a square column Chinee mill despite all the "customer paid, passed QC" issues that came in the box as a Brucie bonus!

For general purpose use the two major problems are the limited vertical axis daylight / travel and the poor grip of the collets on milling cutters. Limited vertical daylight and travel can make setting up for drilling hard work. Need short drills rather than standard jobbers length in most sizes. Not really room for a vice on anything much over 1" thick. Hafta think about the extension of the vertical slideway below the main casting too. Its very easy to end up with an impossible job because the only way to get the cutter over the right part of the workpiece involves passing a higher bit under the end of the slideway and it simply won't go! The simple small knurled hand wheel collet tightener severely limits the grip. Cutters over 1/4" will slip on you if you attempt anything approaching normal feeds and cuts. Not every time but it will get you.

I consider the relatively low speeds unforgivable. You simply can't run the sizes of cutters it prefers to use at anything like the correct speed. Makes for slow work and its easy to break cutters if your attention wanders. The less said about the belt drive system when inclining the head the better. Mine put me on Santas naughty list more than a few times and that had been modified with a swivelling motor mount so the pulleys could be got closer to the same plane. The man who sold it to me was very proud of this modification which "made life much easier". If that was easier lord preserve me from the standard system.

Now given the number built and used it can't be a totally rubbish machine. Bottom line is it does what it does well enough given its era. But it doesn't do well out of its niche. You need to be sure that what you need it for falls reasonably close to that niche if you are every going to be happy with it. Its a deceptive machine if your acquaintance with mills is limited beacuse it looks as if it can handle much larger work than it is designed to or capable of.

Clive.

Edited By Clive Foster on 23/11/2016 17:46:27

Edited By Clive Foster on 23/11/2016 17:47:40

A friend at work operated a "Genie", a big Geneva jig borer with a power driven rotary table about six feet in diameter. The machine was used used for any conventional machining other than grinding including drilling holes, boring, turning and milling. As hinted the machine was not small, it stood about twelve feet high and the table was a good four feet from the floor. And there were built in steps up to the table. There were three of these things in a row and were used for one off jobs, mainly instrumentation work.

JA

On reflection twelve feet is a bit of an exaggeration.

I have found the device: http://www.lathes.co.uk/sip002/page4.html

JA

Edited By JA on 23/11/2016 19:38:44

Interesting description of a novel use for a Jig Borer here

https://sites.google.com/site/rawkinssu/home/windtunnel

The author of this piece has retured by the time I started at Brooklands, but the SIP jig Borers well still in the Wind Tunnel model shop in the 1980's

Edited By Stuart Bridger on 23/11/2016 19:27:01

I was watching a tv programme recently about refurbishing a sports car with a Coventry Climax engine in it. It included an old black and white film clip where a chap was boring a cylinder on a whacking big machine, I'd guess 8 or 9' high. New to me was seeing the operator turning an Allan Key in the boring head while the machine was cutting. The other thing I noticed was that the machine was a "Herbert Jig Mill". Presumably a "Jig-Mill" is a high precision borer that can also do precision milling. Is that right?

Dave

Worked on quite a few jig borers, SIP, Newall, Moore, Huaser etc. The main thing that differentiates them from a mill is an independent measuring system on the x & y axis, usually optical . The lead screw is used for positioning only. Most of them are column type machines as this is more accurate/rigid than a mill knee setup. To call a BCA a jig borer is stretching things a bit as they just don't have the necessary accurate positioning and rigidity.

Michael