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

Hi there,

(apologies, I think I'vetouched on this before, but I need to press on and actually do it, hence more detail needed from this related line of questioning)

I'm making a plate to mount on a stepper shaft...the stepper shaft is 8mm.

Now I want no slop on the plate whatsoever, so I want the hole in the centre of the plate to be a pretty perfect fit - 8mm.

Now I've never really used my lathe that much in anger, so I'm wet behind the ears wrt getting this perfect 8mm hole. The Googling I've done suggests that drilling a smaller hole then either reaming or boring out the hole to size is the way to go.

Which is the easiest, which is the cheapest (tool wise) & HTF do I do it! Seriously, I looked up reaming - and apart from a couple of porn sites (which I enjoyed very much) there's cack all out there illustrating how it's done - does the reamer go in the tailstock? Or if using a boring bar, does that fit in the toolhoder as normal - what size boring bar should I buy for an 8mm hole blah blah (you get the picture ie "this joker should not be allowed anywhere near a lathe", etc)

Thanks for your help.

Hank.

Hi Hank have a look at
http://www.woodwindcourse.co.uk/user...ng_reamers.doc

I hope it helps.

Regards.

Ivan.

Chuck up workpiece in lathe (or clamp to faceplate), drill out 6mm or so, using drill in tailstock chuck. Small boring bar in toolholder, insert into hole taking light cut open hole out to required size. For what you want you can get accurate enough with boring if you use short tool to avoid tool shank bending and use a light cut can cut 0.05mm undersize then trial with stepper while still chucked until tight push fit (if its close enough you can heat workpiece with hairdryer to expand it and it will be a tight fit when it cools). I dont think you need to ream it, but if you do want to, bore out 0.2mm undersize then ream with reamer in tailstock chuck.

Now you have the reamed hole how you going to fix it to the shaft?
Usual way is to drill and tap a hole or holes for grub screws etc otherwise what yo fix will spin on shaft.
Peter

Thanks guys...I now realise I didn't give enough info!

I've just bought a slug of 60mm diameter ali... it's 100mm long off which I will cut a slab of 30mm mount in my lathe to work on.

I will turn don about half of this workpiece down to leave flange on one side of the plate, which will have a grub screw going through it to grip the stepper shaft (I'll put a flat on the stepper shaft).

Therefore this 8mm hole needs to run 30mm deep through my workpiece. So is it possible to buy a boring bar that would go into say a small 7mm hole and allow me to cut 30mm into the ali?

I guess a reamer would be my best option but they seem to run a bit expensive and I'd need one per hole diameter type (I like the flexibility/flexibilty of a boring bar) ...have I git this right?

cheers,
Hank.

PS to refresh your minds (or show those that missed my first time round of questioning!), here's the bit I now need to make out of ali...

http://img160.imageshack.us/i/14811707.jpg/ - ie the round transparent faceplate in the piccie.

The great advantage of boring in the lathe is getting the OD and ID concentric.

Why not make a boring bar? The picture of the ones attached are simple steel rods with a cross hole, to take the cutting tool, and a threaded axial hole to fix it. The cutting tools are ground from broken reduced shank carbide PCB bits.

The smallest one shown here is 5mm Diameter, used to cut the 2" deep, 5/16" ID, LH acme thread for my steady rest support arms.

Yes, you need one like this 5mm head on a 6mm shank (top one on page). If your normal lathe tool is bigger than 6mm then you might want to make up a boring bar holder (or buy one) to hold the cutting edge at the right height.

Boring is not as accurate as reaming, but within 0.05mm is possible with care and light cuts and thats easily good enough for this need.

Only real problem is how you going to measure your progress in boring the hole!
Simplest way is 7.5mm drill and a 8mm reamer just remember to withdraw reamer from hole whilst the bar is turning, never turn reamer in opposite direction as it will enlarge the hole nad possibly damage the reamer.

Peter

The problem with drilling and reaming is there is no guarantee that the reamed hole is concentric as drills cut an oval hole and the reamer may end up off centre.

For small holes like this the best way to check is with the shank of a drill set... a 7.9mm drill (checked with a micrometer) will do as a test... although the stepper shaft is the ultimate test! A bore gauge will also do (6th one down)

Quote:

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Originally Posted by irving2008

Yes, you need one like this 5mm head on a 6mm shank (top one on page). If your normal lathe tool is bigger than 6mm then you might want to make up a boring bar holder (or buy one) to hold the cutting edge at the right height.

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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?

Bill...thanks for the advice about making one, but I'm far too novice at this to think about making a boring bar at this stage (I don't even know how to use one let alone make one!)

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?)

Thanks for your help thus far - I really wish someone had made a youtube video about boring out a whole. (it's no doubt a breeze once youve done it once, but never having even seen the tools I need, it's a little bit hard for me to visualize right now!)

Quote:

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Originally Posted by HankMcSpank

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?

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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)

Quote:

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Originally Posted by HankMcSpank

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?)?

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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


http://www.youtube.com/watch?v=NmeybaCuy7Q

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!

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

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.

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 :smile:)

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.

Quote:

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

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!:eek: 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?

Quote:

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Originally Posted by HankMcSpank

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 -

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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 :smile:

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

A bad photo here...

http://img685.imageshack.us/img685/6551/lathe.jpg

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.

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

Quote:

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Originally Posted by BillTodd

!:eek: 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?

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Dril bits were brand new (they are jobber bits - cheap as chips, but I figured on throwing them away and starting with a new one very regularly)

Yes the lathe is turning in the right direction (BTW, I'm not offended - it's a valid question with someone new like me!)

Re the tail stock alignment - this (I think) may be the root of my problem - how can I check it's alignment to see if it's within tolerance?

Thanks.

Quote:

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Originally Posted by ptjw7uk

Cutting on the retract stroke will make the bar cut better as it is in tension.

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The 'joys' of boring bars on small lathes :rolleyes:

If there's any twist on the saddle the return stroke will cut deeper, I usually switch off before I pull it back. (Myford ML10)

Tempting to use the reverse pass if you want a flat bottom hole because you can run the saddle up to a stop for the next cut, but I don't find boring bars like being pulled sideways in to a deeper cut. They like a bit of X motion to stop them chattering.

If the bar doesn't cut sweet as a nut all the way through on the first pass you have to stop and figure out what's wrong. If the tool height/angle is wrong you can cut a taper.

The bar will flex. If I want an exact size I make several, same depth passes at close to final diameter until it stops cutting, measure, wind the tool out to size then do repeat passes until I get the desired fit. If the material is likely to work harden and I don't have an appropriate reamer, I like to keep the cut depth fairly constant and just hope the flex stays consistant :heehee:

Quote:

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Originally Posted by HankMcSpank

Re the tail stock alignment - this (I think) may be the root of my problem - how can I check it's alignment to see if it's within tolerance?

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Centres in both stocks then nip a thin piece of metal between them.

If it twists you are misaligned :smile:

Cheap 'jobber' bits can be OK. I used a one to drill a 5/6mm 8" through a steel spindle (the 5mm was riveted into the end of a 6" long 6mm rod - I didn't want to wreck a good bit). Just check how they cut and make sure the end is ground correctly.


Boring bars should only be used to cut forwards (make sure you don't drag them back on the final pass).

As Robin said, you should take nice even cuts up to the finished diameter. The finishing pass should be the same depth (since the bar will always bend while cutting; if you try to take finer cut the bar will bend less and you'll take off more than you thought you were going to and probably over shoot the diameter)

My guess your new boring bar is only ground to an approximate shape, so it's ready to be sharpened (since its final shape is determined by the material you are going to cut)

The tool angle should be correct: the tool should cut with the very tip of the tool: the top, front and underside should all slope away from the part.

When you cut, the material has to shear apart and slide along the face of the tool, The material will cut easier if this shear face is at an acute angle. However, as the shear angle gets more acute, the tool gets weaker. The cutting tool shape is a compromise between shear angle and strength (and cutting force).

Soft/weak materials (ones that shear easily) will cut with a low force, so the tool can be acute. Stronger/harder materials need more force to shear, so will need tools the a more obtuse angle (for strength). Beware strong materials that are also soft (e.g. copper and its alloys) they will grab the tool.

You can cut strong/hard materials like steel with a knife like tool - you just need to take a very very fine cut.

The tool should be sharp: I.e. the cutting faces should be smooth, flat and at the same angle all the way 'till the last molecule :naughty: Don't confuse the words 'sharp' (meaning the edge is not rounded) and 'acute' (a tight, narrow angle).

Bill

Thank for you valuable input.

Here's my strategy for now...

1. Order up an MT2 Tailstock ER32 collet holder (on account I already own a full ER32 collet chuck & collets for the spindle....not essential I realise, but they're only £20 inc shipping from China & will be highly useful for some of the small intricate things I want to finally make)

2. Check tailstock alignment!!!

3. Order a full set of centre drills (the one I had was a bit piddly)

4. Order up some new 8mm drills (ie abort the concept of drilling a smaller hole & boring until I become more lathe savvy!)


thanks once again!

Just to give some closure here.

Last night I finally got around to mounting/using my ER32 collect chuck on my mini lathe.

I flipped the workpiece around since taking that photo above (it's 20mm diameter where I've turned it down...which just fits into my largest ER32 collect nicely).

Anyway, my larger centre drill arrived yesterday so I used that & then followed up with an 8mm drill......it's turned out just fine for my needs.

So it was all much ado about nothing rally ...no drilling undersize & then borring needed. (I still need to revisit why the boring tool seems woeful at erhm....boring - for another day though!)

Coming back to why the drill bits wandered - bit of a mystery ...I'd have to think it was something to do with the tailstock not being fully secures &/or centred (I made doubly sure the tailstock nut was tightened extremely well this time...possibly moved during the drilling process last attempt?) & then using the larger centre drill seems to have helped.

And wow...what a difference using an ER32 collet chuck is on my lathe - it's made the whole experience quick & accurate & enjoyable. I no longer have to think "B0ll0****...there's a turning job I need to do, but that *&$*ing 4 jaw....euugh"

That's what engineering is. i.e. whatever is adequate for the purpose. There are pros and cons for all methods.

I have a similar engineering situation and I will be using an undersize drill followed by a reamer. The pros for this is that it is quick and can be used over and over again with consistant results. Like a twist drill the reamer can be used more than once. Also a reamer will make a consistantly parallel hole; this is something to be aware of when boring deep/long holes - is the lathe quality good enough? You don't want to end up with a hole that is ok at one end and tight or slack at the other.

This my part. It's a chopper disc for speed feedback on a spindle motor.
Attachment 8418