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Thread: Help Boring Longish Holes
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14th Oct 2019, 04:37 PM #1Most Valued Member
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Help Boring Longish Holes
Hi all,
This is a what I assume to be a very basic question, yet it's been one I have been meaning to ask every time I need to bore a longish hole.
It seems that whenever I need to bore a long but relatively skinny hole, I have issues with the swarf eventually clogging up and fouling the boring bar cutter. This, at best affects the surface finish because the swarf ends up getting between the workpiece and the cutter and at worst can damage the boring bar.
My latest project being to make a quill handle for my mill. The body will be made from 50mm BMS and the hole needs to be a neat sliding fit on a 25mm shaft. I'm opting to make an adjustable handle such that the main handle will be spring loaded and pulling it in towards the machine will dis-engage the locking pin, allowing 360 degree adjustment to a comfortable angle. Releasing the handle outwards allows the pin to re-locate to the nearest hole.
So, the main body being 50mm BMS and centre bored to 25.05mm and approx. 60mm long has once again presented issues where the swarf eventually gets clogged and fouls the cutter, degrading the internal finish.
It obviously gets better as the hole gets bigger as it allows the swarf a larger volume to eject. But at smaller diameters, what is the best practise?
Do I need to hold a compressed air gun down the guts? Gotta be a better way surely?
Any advice much appreciated.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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14th Oct 2019, 04:50 PM #2Most Valued Member
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If the hole is blind, you just have to stop and get them out regularly. On a through hole I use coolant to drag the chips out the bottom of the hole. I use pretty heavy cutting oil though. Ideally drilling 95% of the hole out means you only have two tedious passes to do.
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14th Oct 2019, 05:35 PM #3
Hi Simon, Guys,
For small precision through holes, I tend to drill as close to size as I can, then ream or "D" bit to finish. The problem with small blind holes is really a peck and clear ! It can get very tedious though. For larger bores, say one big enough to get a 1/2" inch toothbrush head in there, it is the same procedure, drill as much as needed and clean out regularly. Blind large bores tend to be just that large and usually quite shallow, so a stiff paint brush tends to be better. I have one that has been used and not very well cleaned, leaving the bristles stiff and shorter than usual. It gets much harder on the mill, because the swarf tends to build up in the bottom of the bore. I don't use air, since in a small workshop bits get blown all over places you don't want.
HTH.Best Regards:
Baron J.
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14th Oct 2019, 06:36 PM #4Philomath in training
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A task like that I would drill out as much as I can (23mm is around the biggest diameter for a MT2 taper drill) and then bore to finish. Occasionally I blow down the bore of the lathe (that is, towards the tailstock) but I can't recall having to stop to clear chips. The only thing I can suggest is to push your boring bar more so the chip breaker produces small chips that tumble out of the end of the bore.
Michael
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14th Oct 2019, 07:00 PM #5Most Valued Member
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60mm deep at 25 dia I would probably drill close to size and use a 14 to 16mm dia boring bar, material bright mild steel about 400 rpm, if you get chatter drop the revs down.
If the chips formed start to cause a problem by getting caught between the job and the bar start your cut at the other
end of the hole and cut towards the tail stock, with a bit of luck the swarf will curl towards the chuck, or at least not get caught
between the bar and the job.
Sometimes if you have a bit of room between the the bore and the bar you can turn the tool post on a bit of an angle and the
slightly different approach angle can send the swarf curling out the hole behind the bar.
cheers, shed
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14th Oct 2019, 07:01 PM #6Most Valued Member
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What is the cutting tool made from?
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14th Oct 2019, 07:57 PM #7Most Valued Member
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Hi PC,
For this job I was using a 16mm boring bar with a TNMG insert.
But I also have a 12mm boring bar for smaller jobs.
Simon
Sent from my SM-G970F using TapatalkGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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14th Oct 2019, 08:21 PM #8Most Valued Member
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So with that tip is it chipping or giving wire.
You may need to increase your feed rate if it's not chipping,
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14th Oct 2019, 08:36 PM #9Most Valued Member
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Ok. It was chipping and then I back off the feed rate and it gave a continuous ribbon.
Should I keep the feed rate up and keep chips?
Simon
Sent from my SM-G970F using TapatalkGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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14th Oct 2019, 08:37 PM #10Philomath in training
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Yes
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15th Oct 2019, 09:41 AM #11Most Valued Member
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When you increase the feed rate to get chips on a small hole the chips cling to the bore
and deposit themselves on top of the boring bar, they build up and can wedge between the bore and the bar,
increasing the angle of the boring bar will open up the gap and the angle also seems to help the chips flow away a bit better.
Personaly i only do that on larger bores where surface speeds are lower and the chips dont stick to the bore and they flow nicely out the hole.
One thing you also have to remember that the more force you put on the bar the more it will flex, so you have to be carefull to make allowance for that
when coming up to your final cut.
On small holes i prefer to make long curly swarf, most of the time you can get it to
come out one way or the other and it does not jam between the job and the bar, or at least it is less likely to, and
clean up between cuts if need be.
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15th Oct 2019, 11:54 AM #12Golden Member
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Harold Hall Idea - might help you
In a Workshop Practice Milling book Harold Hall suggested the following - its not an exact quote just what I remember as being the guts of his idea.
"It can be difficult to bore a long true accurately sized hole. What you can do is accurately drill/bore a shallow oversize hole at each end, then bore the through hole, and then put in an insert or a bearing of the correct diameter at each end."
You then have an accurately placed and sized hole at each end and a less accurate bored through hole.
It is in his Milling book in the dividing jig section if you want to see his exact words.
Bill
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15th Oct 2019, 06:25 PM #13Diamond Member
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I have finished holes by starting the cut at the inside end of the bore and feeding out of the hole (i hope this makes sense). But i don't think it will work with tnmg inserts, i have only done it with tpmt inserts.
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16th Oct 2019, 01:11 PM #14Most Valued Member
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This blind hole is about 31mm dia, 58 deep, triangle insert, 20mm dia bar on an angle, 4140, 400 rpm, feed is .082,
DOC .5mm.
As you can see the swarf comes out to the rear of the boring bar, sometimes i squirt air in the hole to clear swarf and sometimes stop half way or even nearly at the end of cut as a wad swarf might have built up at the end of the bore.
The point is here is that by making swarf and not chips the cut surface is not getting damaged.
Cheers, shed20191016_121627.jpg20191016_120708.jpg
Sent from my SM-G900I using Tapatalk
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16th Oct 2019, 03:57 PM #15Most Valued Member
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Thanks shed, Thanks everyone for your replies.
I redid another hole and used some of the ideas suggested. I still found the best results were to use compressed air to blow the chips through and out the other end if the headstock.
Simon
Sent from my SM-G970F using TapatalkGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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