# Jig Borer - I reveal my Ignorance and Stupidity



## Nick Hacking (Nov 11, 2017)

Dear All,

I decided to get into hobby machining a couple of years ago. I started off with a small refurbished British lathe. Of course, I soon decided that I needed a mill and I started looking through eBay for an affordable mill close to my home.

Eventually a lovely little BCA jig borer popped up and I smuggled it into my workshop when my wife was out. Of course, I soon found that using the little machine for anything like heavy milling was a serious abuse of the poor thing, so *another* covert operation had to be organized to get an old Bridgeport into the workshop.

So far, so good. I've been learning by doing, reading on here, watching YouTube. I've made a couple of toolposts for my lathe, some T nuts, a lot of chips. But, I've now got this little jig borer sitting in a corner of the workshop _and I don't really know how to use it at all._ I understand that it's good for precision work and that, these days, it's largely been superseded in industry by CNC and electronic control systems on mills. But, what I cannot find are any helpful tutorials on how to use it properly. There's plenty of material on milling and on running a lathe, of course, but nothing really on "projects for your jig-borer".

Is anyone able to offer me advice? Are there any resources I can learn from? Perhaps old text books.

I want to use the beastie, it would be a shame to simply let it rust away, but I don't want to abuse it. In short, I've bought something that I don't really understand and I've decided that it's better to confess and learn than to continue in my ignorance.

Kind wishes,

Nick


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## Bill Gruby (Nov 11, 2017)

Workshop Practice Series #35 --- Milling - a complete course.  This book will get you well on your way.

 "Billy G"


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## Nick Hacking (Nov 11, 2017)

Bill Gruby said:


> Workshop Practice Series #35 --- Milling - a complete course.  This book will get you well on your way.
> 
> "Billy G"


Off to Amazon right now.

Many thanks, Billy G.

Nick


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## HMF (Nov 11, 2017)

No ignorance or stupidity on here, just questions needing answers.


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## Eddyde (Nov 11, 2017)

From what I understand they are used for drilling holes at very precise locations.


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## Billh50 (Nov 11, 2017)

Having run a jig bore many times in the past. I can say this. They are mainly used for precisely locating holes. But can also do light milling to locate slots and other features. As well as widing slots to precise dimensions.


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## Nick Hacking (Nov 11, 2017)

Nick Hacking said:


> Off to Amazon right now.
> 
> Many thanks, Billy G.
> 
> Nick



Hmm,

A quick trawl through my shelves and I find that I've actually got this book already. It _is_ a very useful introduction to milling, but there's nothing really specific to the jig borer, that I can see. Are there any textbooks with advice specific to jig boring machines?

Kind wishes,

Nick


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## Nick Hacking (Nov 11, 2017)

Billh50 said:


> Having run a jig bore many times in the past. I can say this. They are mainly used for precisely locating holes. But can also do light milling to locate slots and other features. As well as widing slots to precise dimensions.



Might I ask what sort of projects you used your jog borer for?

Nick


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## Bill Gruby (Nov 11, 2017)

You will find nill to nothing about using the Jig Bore to mill. It is a specific machine for boring holes. Yes Bill is correct, it can be used for light operations but that is not what it is for. We had 12 Moore Jig Borers at GM. They were in a temperature controlled room. No other machines were in there with them. These machines are sensitive to side pressure. You can throw the spindle off center in a heartbeat.

 "Billy G"


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## Billh50 (Nov 11, 2017)

BillyG,
According to Moore they can be used for very light milling. We have used them in the past for only removng a few thousandths to qualify surfaces and slots as well as locating holes. Never had a problem with throwing the spindle off.

Nick,
I was a special machine builder before I became a special machine designer. Then when that company went under due to owner having an accident, I went back to being a toolmaker until I became disabled.


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## Bill Gruby (Nov 11, 2017)

Yes Bill they do, but it is not recommended practice. You won't throw it off as in the spindle off the machine but you will throw the accuracy off if you push too hard. That's why they call it a Jig Bore and not a Jig Mill or Universal Mill. LOL

 "Billy G"


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## Billh50 (Nov 11, 2017)

True. it is only for very light milling. Never did push em when milling.
For hole locations they are great. Ran a jig grinder also for locating and sizing holes after heat treating.


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## Nick Hacking (Nov 11, 2017)

So when I want to make a hole (or series of holes) at a precise location (or series of precise locations) I should load up the jig borer with either a drill bit or an end mill and use it for making accurate vertical holes, using the x,y and z indices and my rotary table as required.

Once I start doing any milling operation where there's _sideways_ force on the tool, I should stop and think if this isn't an operation better done in the Bridgeport?

Is that a fair synopsis?

It can hold tooling up to about 12 mm diameter, and of course, using devices such as fly cutters, it could handle bigger holes than that. But always where there's little or no sideways cutting: just straight up-and-down?

It is a fairly small machine, especially in comparison to the mill.


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## Billh50 (Nov 11, 2017)

You got it. Only milling that should ever be done on a jig bore is only a couple thousand removal. Just a finish cut. Any more and it can throw things off.


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## Nick Hacking (Nov 11, 2017)

Nick Hacking said:


> So when I want to make a hole (or series of holes) at a precise location (or series of precise locations) I should load up the jig borer with either a drill bit or an end mill and use it for making accurate vertical holes, using the x,y and z indices and my rotary table as required.
> 
> Once I start doing any milling operation where there's _sideways_ force on the tool, I should stop and think if this isn't an operation better done in the Bridgeport?
> 
> ...




This is it.

To show the scale I've put a 14 mm spanner (wrench) on the table.

It's very simple: the spindle is fed from the motor via an idle wheel. Different combinations of drive and driven pulley wheels can be selected to alter the speed, in the usual way. The head can be tilted in the coronal plane (but not saggital). The knobs on the top move the spindle in the Z-axis. The two on the side facing the camera move the table in the X-axis and rotate the table. The knob on the front of the machine moves the table in the Y-axis - and that's all there is to it: a sort of elegant simplicity.

Thanks again for all of the advice,

Nick


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## Billh50 (Nov 11, 2017)

That's a cute little thing !


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## Bill Gruby (Nov 11, 2017)

It looks like a Watchmakers Jig Bore. Mucho Precision.

"Billy G"


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## rzbill (Nov 11, 2017)

Went to Moore years ago during a project. For me, it was like going to the 'church of precision'.  I felt like kneeling and chanting "I am not worthy". 

Nice machine you have there although may not be applicable to the needs of most hobbyists.


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## benmychree (Nov 11, 2017)

I had a Pratt & Whitney #3 jig borer in my shop and used it for anything but jig boring; it was large capacity and had all geared speeds with a 4 speed motor; we used it as a big milling machine.  Sadly, after I sold the business, it was scrapped.


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## Nick Hacking (Nov 12, 2017)

Thanks for the kind comments, all.
I hope you can see, now, why I want to use it but definitely _don't_ want to abuse it.

The jig borer was about half the price of my old Bridgeport. If I had bought the Bridgeport first, I'd never have spent the money on it but I'm really glad that things turned out as they did because it's not the kind of thing that I'll ever voluntarily part with. I suppose that's the great advantage of being a _hobby_ machinist: I can afford to allow sentiment and emotion into my decision-making. I'm not doing this for a living (if I did, I'd be a lot thinner than I am right now).

If I come up with a project that can use the jig borer's capabilities sensibly, I'll post it up on this forum.

I really appreciate the advice and encouragement that I've had on here. Thanks again to all of you.

Kind wishes,

Nick


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## jamby (Nov 25, 2017)

I don't know if this will add much but here goes.   I ran several jig borers when I worked in the tapered and miss-located hole room.  The P&Ws were like big bridgeports without the knees and the Sips were gantry's with a column on both sides of the table. Had to wear sweat shirts even in the summer, 68 deg.  The big Pratt & Whitneys used rods and mic heads to measure distance and the Sip's used scales and optics.  They were used to locate holes in exact positions and bore them to tenths tolerance, checked with bore gauges.  We did a lot of tooling plates, some of these we could ream if the tolerance was loose enough, like slip or press pins.  But the real trick was the precision boring heads as they would hold tenths and leave great finishes.  
All the tooling around the area were high precision,  angle plates, 3,4,6 blocks, dividing heads,  rotary tables.  One of the jig bores in another shop was a Dixi it was set up like a boring mill with a rotary table built into it.  
My favorite was the smaller Sip because of the type and size of the work.  The only complaint was you had to sit side-saddle because of the location of the column and head.  But neat machines.

emm..  bore gauges were set by the tool room for size and we read them by placing them in the bore like a telescope gauge but you read the size as you rocked it back and forth on the dial gauge.  They came to us with a master block set to the nominal size we wanted so we could make sure they were still correctly set.

Jim


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