Need a perfect 8mm hole - to ream or bore?

[irving2008]

Ok, I'm seriously beginning to doubt my ability to visualize things here - that boring bar you linked to has a round shaft, but boring bars mount into the tool post? (which needs flat/square sided tools) - therefore there must be a boring bar holder with square edges in the equation?

Thats correct... depends what size tool your lathe takes... could be as simple as grinding a flat on the bar, or a piece of square material drilled out 6mm with a locking screw. You can also get flat sided boring bars but not usually for that small a diameter hole although Chronos do one (second from bottom)

Pete - re measuring the progress through the hole - well my mini lathe has DROs I figured it'd just be a matter of zeroing the DRO as the boring bar enters the hole and then taking it thru in until the DRO reads 35mm - that way I know I've cleared the hole? (or again am I missing something here?)?

I think Pete was refering to the hole diameter, but if you have a DRO then its easier, just dont rely on DRO for final diameter. Hole depth is as you say... assuming the centre hole in the chuck will clear the bar...

Found this video, its a start, there is a better one I have seen but can't find it right now

[HankMcSpank]

Thanks Irving - some really helpful input you've given there.

So it seems that I'm going to have to shell out a bit of cash ....& here was me buying a lathe to save a few bob!

Audio Andy has kindly offered me the loan of a small boring bar - so unless Ebay turns up a cheaper option to the Chronos Route (having to buy a boring bar holder as well as a suitable boring bar is frankly just taking the p***!), then I'll likely take Andy up on his kind offer.

Many thanks to all who chimed in!

[ptjw7uk]

HankMcSpank I think you have just began to realised that getting the lathe is just the start, there is an seemingly endless variety of tools and attachments for the lathe. For my boring bar holder I used some square stock that would fit in the tool holder put a large drill in the 3 jaw chuck and pushed the metal against the drill, then drilled and tpped 2 holes perpendiculer to the hole to hold the bar in place voila, one holder.
My biggest problem is in finding suitable stock to make things usually for a few £'s more I can get the article ready made at times it dont make sense in that the finished article can come from china but a bit os steel jst down the road costs an arm and a leg plus postage!

Keep up the learning process
Peter

[HankMcSpank]

In the end I bought a micro boring bar that irving linked me to above (cheap enough not to have to make my own)....

http://cgi.ebay.co.uk/ws/eBayISAPI.d...=STRK:MEWNX:IT

I'll knock up a tool holder myself - that bit should be quick/easy/dirty.

Many thanks for all your help.

Hank.

[HankMcSpank]

Ok, I'm now actually workjing on the bit that needs an 8mm hole - HELP!

So the story so far. I need a backplate for a pickup wider. I eventually take delivery of 100mm length of 60mm dia round aluminium bar - & I cut 35mm off the end (with a hacksaw - I've a bicep like Popeye now) . I then true it up in my 4 jaw ...it took me absolutely ages - top tip, make sure the jaws are inserted the right way for the size of the piece becuase for all the jaws sorta gripped the piece in their original way...and the piece went in ok, the jaws were almost totally out their holder - their threads hadn't sufficient purchase into the chuck, meaning the jaws were locking up as I tried adjusting them)

Anyway, so the first part went well (turning down about two thirds of the overall length down to about 20mm thereby making a flange type of arrangement (aren't engineering forums great - you get to use all sorts of double entendre sort of words )

All this left me to do was drill a simple hole through the middle of the workpiece - piece of p!ss me thinks - hah, not at all - AAAAAAARGHH. You'd think it would be easy, but what I got was a hole that was all over the shop - and that was starting with a centre drill.

I removed the centre drill & then put a normal drill - the thing bends flexes like a b1itch (not a double entendre - just a bitch) - am I meant to use a special type of drill ...maybe stubbier, shorter?

So anyway, I stop after drilling in to the piece about 5mm, panic and instead of using a 7.5mm drill , (I need an 8mm hole)...I slap in a 6.5mm drill - it bends about like a bendy thing in Bendy Convention....no worries thinks me - I'll kick this holes backside & play my trump card - my Micro boring bar!

So after making up a shoddy boring bar holder (I'm too tight to buy a proper one), I start using that, thinking it would be a dream/breeze - AAAAAARGH. This things starts flexing a litoo - I've had to abort the mission for this evening on account I'm ready to torch my lathe - but what's the score with boring bars - is there a technique I'm missing?

If I get a chance I'll post a photo later.

[BillTodd]

I slap in a 6.5mm drill - it bends about like a bendy thing in Bendy Convention.

! in ally???

Are your drills sharp? Is the lathe turning in the correct direction?:rofl:
Is the tail-stock aligned correctly?

Drilling a hole in aluminium should not cause you any problem. Similarly, if your boring tool is sharp, it should easily cut a clean hole.

What depth of cut are you trying?

[Robin Hewitt]

So after making up a shoddy boring bar holder (I'm too tight to buy a proper one), I start using that, thinking it would be a dream/breeze - AAAAAARGH. This things starts flexing a litoo -

Either the tip angle is wrong and it's rubbing below the cutting edge
or
The tool height is wrong, slightly above centre is better than slightly below
or
The cut is too deep for the whip in the shank
or
You haven't got a good grip on it
etc

[BillTodd]

Ok this is not ideal but have a look at the first few frames of this video - it show how the tool should be shaped

http://www.youtube.com/watch?v=ieZ0OMa39Ok

The tool should be razor sharp, just like a wood cutting tool ( i.e sharp enough to draw blood when you catch the back of your hand on it while checking the bore ;))

BTW these little lathes will benefit greatly from being bolted down (and shimmed to be square) to something heavy and rigid (2" of heavy plywood -layered would be good)

Found these good tool bit sharpening videos while looking for a boring bar sharpen video:

http://www.youtube.com/watch?v=hrDr4rYLiAk
http://www.youtube.com/profile?user=...26/dRyqIm5JR5s
http://www.youtube.com/profile?user=...24/HTQ46NMMc88

[HankMcSpank]

A bad photo here...



here's the boring bar I bought...

http://cgi.ebay.co.uk/ws/eBayISAPI.d...EOIBSA:GB:1123 (you can enlarge their advert piccie a bit by clicking on it)

Re being sharp - hard for me to say, it was brand new out of its holder tonight?

I had a look at the video - big difference to my boring bar - which flexes - also I note he takes the tool in, and then cuts as he retracts - I noticed myself that the boring bar seemed to cut better on the return leg - what gives?

Anyway, I'm gutted ...yeah, yeah I should have practised first, but for chrissake - it's an 8mm hole, & there was nothing in the manual about it taking me all night & still screwing it up! (& I'm not sure it can be rescued as the first 5mm depth into the hole is greater than 8mm now (I can feel another Popeye sawing session coming on)

I'm gonna take up stamp collecting.

[ptjw7uk]

Hank,
Cutting on the retract stroke will make the bar cut better as it is in tension. Your bar looks quite fat for the size of hole and could be rubbing near its bottom, it is quite important to get the clearances right but its ultimately a trade of against size and rigidity as the larger the hole the larger the cutter.
This is why I think most small holes are finished with a reamer.
Also somethings wrong if the drill is flexing all over the place, I've had it happen when the drill was sharpened off axis(ive a lot to learn about sharpening)
Peter