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  1. #1
    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.


  2. #2
    Kn8's Avatar
    Location unknown. Last Activity: 10-11-2014 Has been a member for 7-8 years. Has a total post count of 58. Received thanks 1 times, giving thanks to others 0 times.
    Hi Hank have a look at

    I hope it helps.



  3. 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.

  4. #4
    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.

  5. #5
    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?


    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... - ie the round transparent faceplate in the piccie.
    Last edited by HankMcSpank; 04-01-2010 at 09:52 PM.

  6. 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.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. 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.

  8. #8
    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.


  9. 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)

  10. #10
    Quote Originally Posted by irving2008 View Post
    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.
    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!)
    Last edited by HankMcSpank; 04-01-2010 at 11:11 PM.

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