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Boring on a light mill

Advice on depth of cut etc

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ChrisB12/04/2019 12:03:05
304 forum posts
123 photos

Hello everyone, I have a question regarding boring on a small milling machine, I have a WM18.

Before buying a proper boring head (there are many different types, sizes and prices!) I thought I'll mock up something simple just to gauge the machine's limitations etc. I used a fly-cutter body I already had and machined a 12mm dia boring bar using a ground drill bit for the cutting edge.

It seemed to work fine on light cuts of say1mm off the diameter, but when I tried to up the depth of cut to 2mm off the diameter I could see the mill head sort of moving - just a little bit but that cant be right no?

I was boring a hole approx 18mm diameter, 40mm deep at about 250rpm, material not sure what exactly but it was a 46mm diameter 8.8HT

The tool seemed rigid enough with no nasty chattering etc, and it cuts ok, after a couple of passes the cutting edge is still sharp. Any advice is welcome, thanks.

Chris

Ian S C12/04/2019 12:20:31
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7390 forum posts
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Just keep to light cuts, even .25 mm to .5 mm is OK, it just takes time. Patience is what is needed. I'v often wondered if I could do a better job boring cylinders for my hot air engines on the mill, rather than on the lathe as I do now.

Ian S C

David George 112/04/2019 12:30:13
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815 forum posts
282 photos

Hi Chris I have a similar Chester mill and have no problem boring just bought bog standard boring head no problems.

20190326_084614.jpg

David

ChrisB12/04/2019 12:35:16
304 forum posts
123 photos

Is that a 2" head David? and what speed do you run it at?

David George 112/04/2019 12:55:18
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Yes it's a 2" and it depends on what material and diamiter I am boring small hole faster maybe 750 rpm and 6inch diamiter 150 rpm. Also brass and ally faster than hard steel. A good strong boring bar is essential if it comes with a set of boring bars they will need grinding with a green grit or diamond wheel. I make bars for different jobs.

David

JasonB12/04/2019 13:03:23
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On My X3 with a 2" head I seldom take more that 0.050" ( 1.3mm) off diameter which is one turn of the dial.

I would say 2mm is getting a bit much and the HT bolt won't have helped, I'd be running faster than you but with boring heads it is often the balance that will govern your speed not what the book says..

ChrisB12/04/2019 13:34:13
304 forum posts
123 photos

I see, I was doing it all wrong then, will try a higher speed and less depth of cut (which is a hit and miss with my current set up!) What sort of boring head do you reccomend?

I have seen this: **LINK** which will need a replacement arbour

and this: **LINK** which should be a direct fit on my mill. Are these any good or there are better options?

John Haine12/04/2019 13:48:30
2543 forum posts
132 photos

The first would be much preferred if you can get it, but the arbor (which is not a leafy glade) may not be easily replaceable. I have a small Arrand boring head and one of the generic 2" jobbies, the Arrand is a joy to use but the big one decidedly hit and miss on getting an accurate feed.

Douglas Johnston12/04/2019 15:46:20
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580 forum posts
32 photos

When using a boring head in the mill is it better to provide the downward feed with the head locked and using the quill or the quill locked and using the head feed. I have used both methods in the past with success but have often wondered which way is best from an accuracy point of view.

Doug

SillyOldDuffer12/04/2019 16:11:54
4415 forum posts
957 photos

Posted by ChrisB on 12/04/2019 13:34:13:

...

and this: **LINK** which should be a direct fit on my mill. Are these any good or there are better options?

Chris's link took me to a ordinary looking boring head about twice the size of the one I use on my WM18 but otherwise typical of the breed. I noticed though it's described as a 'Rough Boring Head', a term I don't understand. Is it just that it's hefty enough to take roughing cuts, or - can't imagine why not - it somehow can't produce a good finish?

I bought a smaller head thinking it would take up less space. No doubt it isn't as rigid as a 3" head which can also bore bigger holes as well. Am I missing something about small vs big boring heads?

Dave

Edited By SillyOldDuffer on 12/04/2019 16:15:09

ChrisB12/04/2019 17:36:00
304 forum posts
123 photos

This is what I'm using at the moment - no control whatsoever on fine adjustment just guess work, but for the current project it's fine.

20190412_173951.jpg

20190412_174110.jpg

20190412_174129.jpg

But I want a proper one for better control - the one in the last link is quite big true, not sure it's fit for a WM18, price is good...not sure about the quality tho!

PS: sorry for the inverted images!

Bazyle12/04/2019 17:39:44
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4590 forum posts
185 photos

Boring is just turning inside out with a less rigid machine.

What sort of lathe does your mill head look like if it were all turned on its side? Perhaps a 3in lathe with a ridiculous 8in centre height. How rigid is that?
If you were turning mystery metal or 8.8 bolt in this 'lathe' would your first cut be 40thou ? I'd be starting at 10thou or less to see how it performed.

JasonB12/04/2019 18:24:13
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Tool looks blunt in the last photo, also make sure the back edge does not rub on the holes sidewall.

ChrisB13/04/2019 10:45:52
304 forum posts
123 photos

Thanks Bazyle, you're reasoning is obviously right, should have thought of that silly me!

Jason , true the bit looks blunt in the photo, but in reality it is sharp...ish, the bit is a 3.9mm drill bit so it's a bit small. The thing with boring at small increments is it going to take a very long time without having the hole predrilled with a close enough dia drill.

JasonB13/04/2019 11:26:48
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Chris if that is the shank of a 3.9mm drill then they are not as hard as the business end and will soon lose the edge, just think of how easily a drill shank is chewed up if it spins in a chuck. If you are going to regrind old tools then ctr drills or end mill shanks will be fully hard all the way along.

ChrisB13/04/2019 13:19:38
304 forum posts
123 photos

I noticed that, the first try was a common twist drill...which as you say was pretty useless, so I used a stub drill, the hacksaw and file slips off it so I think it's "ok". Bored the hole from 12 to 22mm without issues.

Will see if I can find some larger drills to reduce the "boring" time!

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