Finish inside a bore

I'm trying to machine a cylinder liner from a nice piece of 50mm cast iron
bar from folkstone engineering. All done, but I can't get a good finish in
the bore. I'm about 0.15mm from size now and rapidly running out of road!
I've tried a Glanze boring bar with CCMT type tip and a standard boring bar
with a brazed carbide tip and a whole range of different speeds. I'm spot
on centre with the tip.
Difficult to describe the finish, but 0.15mm should be enough meat to sort
this out.
Any thoughts on how to get a good finish?
Reply to
Steve W
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I use Glanze tools on my Myford Super 7B but I always polish the tip on my diamond wheel before I use it , it gives a much better finish that way. Good luck.
Reply to
If you have only 0.15mm left on dia or even per side you are going to struggle with carbide to hit the size and achieve a finish.Either grind up a bit HSS or borrow a David Brown reamer.The DB reamer will let you creep up on the size very easily. Mark
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Reply to
Carbide isn't the right material if you are trying to creep up. To use carbide correctly you have to have loads of rigidity and a deep cut to get it to work.
In your situation I'd do away with the top slide and mount the biggest boring bar possible directly on the top slide. Fit this with a honed HSS bit with just a tad of radius. Run as slow as possible as regards feed and speed for that last cut.
Let us know how you get on. Keep everything as short and rigid as possible. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:-
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Reply to
John Stevenson
I would add that the default CCMT tip seems to be the CCMT060204. this is not a good tip for fine work on our little lathes. The CCMT060202 has half the corner radius and will deflect less with thin cuts. It still isn't sharp HSS, but it's better. If it needs a polish, you are less likely to break through into the chip breaker groove when trying to sharpen it up.
Mark Rand RTFM
Reply to
Mark Rand
I often find with boring bars that there's a difference in finish depending on which way you feed. Try feeding away from the chuck if you've been feeding towards it up till now.
For a cylinder liner I'd have thought you'd want to finish it by honing anyway.
Reply to
Dave Baker
I have a set of boring bars (with carbide inserts) that _sometimes_ cut like a charm, and most of the time drive me nuts. I made the same obervation like you did. I'd really like to know what the reson is.
I guess it is a too big tip radius. Anybody got a comment / tip?
And yes, if I need the hole in tight tolerances with a smooth surface, I use HSS with aggressive angles, polished knife and low RPM + feed plus cutting oil. I get long curly chips (looking like compression springs) with a diameter well below 1mm. That is nice. :-))
Reply to
Nick Müller
--Howzabout using a cylinder hone? They're cheap at auto parts stores and they do a dandy job. I use one all the time on my 5-A and it really is fast.
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