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Thread: Improving boring heads

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    [email protected] tonyfoale's Avatar
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    Improving boring heads

    A little while back I posted a thread about motorcycle cylinder boring which used an indexable carbide tip.
    Cylinder boring without a cylinder borer.

    This post is about that and some other improved boring cutters.

    Improving boring heads-criterion.jpg
    This is a genuine Criterion boring head with a set of boring bars.

    A genuine Criterion like this comes in at around US $5/600 for a 2" version, but Indian made clones are about 10% of that. Whether clone or genuine article, often the main problem is flex in that style of boring bar due to their length and small diameter. As with any machining operation, rigidity is key to good results. For boring short holes or large holes we have the opportunity of doing better. In the bottom of the head there are two 1/2" tool mounting holes with grub screws, one hole is for boring small diameters and the other is used for larger holes. A more rigid way of holding the tool is to use both holes together to hold a rigid block with an indexable carbide insert.

    Improving boring heads-boring-01.jpg Improving boring heads-boring-02.jpg
    On the left we see the end of a boring head with the two tool holes and one of two insert holders fitted with two 1/2" bars. The other image shows both holders that I made.

    Holders very much like this are available on the net at reasonable prices, so why make your own? Well I have two "identical" clone boring heads but careful measurement showed that the hole centre distance was a few thou different and both were a few thou different from the measurement that I saw quoted for a "for sale" item. Therefore, it was unlikely that a bought one would fit properly. I have several large hammers but their use is not authorised for abusing boring heads. So I made the holders to match one on my two heads, accepting that they would not fit the other head well enough. That was not a big deal.

    Improving boring heads-boring-04.jpg
    This insert holder is for relatively shallow holes from 24 to 55mm diameter. A lot of my precision boring is for bearing fitment and this is perfect for that. I do not need a lot of overhang because the holes are not deep.

    Improving boring heads-boring-03.jpg
    Above is the insert holder for larger holes, which can also be deeper because it will only be the mill quill which will limit depth. Because the centre between the two tool mounting holes is offset, it allows me to reverse the mounting of my insert holder, which gives two diameter ranges. On the left the holder is mounted to cover the diameter range 66 to 117mm, whereas the other mounting position can cover the range from 52 to 70mm.So between the two holders I can cover the range of holes from 24 to 117mm with a very rigid setup.

    This is the insert holder that I used in a lathe as described in the previous post about cylinder boring,
    Cylinder boring without a cylinder borer.
    in that case the boring head was fitted to a very rigid bar instead of the R8 mandrel.

    Improving boring heads-boring-02.jpg

    I made another relatively rigid insert tool for creating 45 deg. chamfers etc. by turning down a lathe tool. My requirement for this tool includes working in some recesses deeper than needed above, so it is longer but kept to the maximum diameter for rigidity. Shown next.

    Improving boring heads-boring-06.jpg Improving boring heads-boring-05.jpg

    Improving boring heads-boring-07.jpg
    This shows the 45 deg. tool being used for a very difficult application. I was making an aluminium motorcycle petrol tank and I welded in the base of the filler instead of the usual method of bolting it on. It distorted into an oval shaped hole, which would not have sealed. So I mounted the top sheet on the mill as best as I could. The surface that needed truing up was at 45 deg. but the required width of cut was only a touch less than the side of the insert. So it was a full width cut on a 2mm thick piece held in place with 1mm sheet. Hardly surprising that there were some small chatter marks but minor. That was a severe test of the boring bar and I was happy with its performance.

    Soon after doing the above, I came across a Narex boring head which I just had to have. It cost me the price of two genuine Criterion heads but it is a beautiful thing.

    Improving boring heads-s-l500.jpg

    Almost complete in its original box, just two tools missing as can be seen by the empty compartments on the LHS. These heads were designed prior to CNC and can do amazing things. You can bore taper holes which otherwise would be next to impossible without CNC. It will cut internal grooves, which of course could be done with a Criterion style head and a rotary table, but the Narex does it without a rotary table. It also has a very sensitive adjustment, ideal for sizing accurate holes.

    Thanks for watching.
    Last edited by tonyfoale; 01-23-2017 at 02:57 AM. Reason: Spelling

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    Ed ke6bnl's Avatar
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    I was just thinking of making a chamfering tool from some odd triangular inserts I had. This let me know it would probably work hope for no chatter though. Nice rigid set you made I like it.
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    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by Ed ke6bnl View Post
    I was just thinking of making a chamfering tool from some odd triangular inserts I had. This let me know it would probably work hope for no chatter though. Nice rigid set you made I like it.
    Ed,

    The chatter that I mentioned was a result of the non-rigid work piece not the tool. There has been no sign of chatter on any other work. It has been a very useful tool.

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    olderdan's Avatar
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    Great idea to use both tool holes for mounting, also eliminates any chance of the tool rotating against one grub screw.
    Should be commercially available, by the way I have been wondering since your original cyl-boring post how you hone them after boring.
    regards
    Olderdan

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    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by olderdan View Post
    Great idea to use both tool holes for mounting, also eliminates any chance of the tool rotating against one grub screw.
    Should be commercially available,
    I mentioned that they are commercially available but the problem is the hole spacing, that needs to be spot-on.

    Quote Originally Posted by olderdan View Post
    by the way I have been wondering since your original cyl-boring post how you hone them after boring.
    I use a conventional cylinder hone and finish with a Flex-hone. I don't recall where I bought either but check out
    Standard Engine Cylinder Hone and
    Standard Cylinder Bore Flex-Hones 3" and up

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    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by olderdan View Post
    by the way I have been wondering since your original cyl-boring post how you hone them after boring.
    I didn't always have the right tools, so in years past it was home made. Back in my teens when I couldn't afford a proper hone I made my own using old pistons. I would cut them in half vertically, fore and aft, mount them on a short shaft through the gudgeon pin holes, with a loose fit. Over that shaft was a compression spring to force the two halves outward. From the lateral centre of that shaft I would mount a drive shaft (~6mm) at rt. angles, this would be maybe 250/300mm long and I'd drive it with a drill.
    To use, I'd cover the piston with valve grinding paste and run it in a dummy cylinder to charge the piston with abrasive. Abrasive particles would become embedded in the relatively soft aluminium. The "hone" would then be ready to use. This type of "hone" was only suitable for finishing the surface, it would not be able to remove a significant amount of metal. I had to bore the cylinder very close to size in the lathe first. With "proper" cylinder hones it is common to remove several thou for sizing after boring. Personally I see no point in leaving that much to hone out and I aim for a thou on diameter.

    PS. This technique requires a full skirt piston, slipper pistons would not be suitable. The main contact is on the side of the piston halves and slipper pistons have no sides.

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    Thanks tonyfoale! We've added your Boring Head Modification to our Machining category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Thanks tonyfoale! We've added your Insert Holder to our Machining category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Thanks tonyfoale! We've added your Chamfering Tool to our Machining category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Sorry for taking so long to reply.
    Thanks for the insight to your early lapping technique I can see how that would work well.
    I totally agree that machining as close as poss to size is the way to go, hand working can compromise the outcome if overdone.
    I understand lapping processes quite well as I used to work Delphina machines and work in the hand fitting shop.
    Regards
    Olderdad

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