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Fly Cutting

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Steve Withnell22/10/2011 13:19:10
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858 forum posts
215 photos
I've never done any flycutting and my current project calls for two surfaces to be skimmed with a fly cutter.
 

So I got one of these indian ones on a MT3 taper and had a practice run:
 

With this result
 
So I thought what I really need is an M&S flycutter, but turns they don't sell flycutters so I made my own:
 

Lots of rigidity, lots of mass in inch square bar and momentum too at high rpm. Result:

(The nasty bits at the bottom are previous drilled holes in the scrap)

Result:
 
I've taken cuts upto 1.5mm and the finish is less good, though still good.
 
Steve
_Paul_22/10/2011 14:45:37
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543 forum posts
31 photos
Hi Steve,
 
If you ran the bought flycutter with the tool steel hanging as far out as the pic shows the finish you got isn't surprising
 
Also Looking at the tool steel in your bought cutter is it the right size looks a bit thin in the pic? if it is that wont help either.
 
In my experience if the tool edge is out beyond around 1/2 the width of the cutter body using 1/4" tool steel (or carbide tipped) the finish starts to suffer depending of course on speed, material, lubricant & depth of cut.
 
Your home made cutter is impressive, a 1.5mm cut with a flycutter is quite heavy.
 
Regards
 
Paul
 
 
wheeltapper22/10/2011 16:09:10
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424 forum posts
98 photos
Hi Steve
did you use the cutter with the pointy end that they come with?
I've got the same sort and I got a much better finish by rounding the end off a bit.
 
Bogstandard has a thread about it somewhere but I cant find it at the moment but I followed his idea, the finish on my engine crankcase is straight from the flycutter.
 
BTW if you flycut ali, use wd40 to lubricate, comes up lovely.
 
Roy
Steve Withnell22/10/2011 17:25:39
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858 forum posts
215 photos
I cut the piece dry, so I'll break out the WD40 and see how that works out.
 
The Indian flycutter slot would take a bigger piece of tool steel than 1/4 inch, but not much.
 
 
I had thought taking light cuts I'd get away with it. Clearly not. I was going to set it up in the mill and run a 10mm slot drill through, as I needed much more than 1/2 inch overhang. At that point I thought I might as well make something more solid.With my M&S version I'm going to creep up the depth of cut and see what happens, 1.5mm wasn't bad at all.
 
Roy - did you spot what my piece of scrap was?
 
 
 
 
colin hawes22/10/2011 18:01:45
570 forum posts
18 photos
Hi Steve, I agree with the previous comments and would like to add that the workpiece needs to be well suported underneath by packing if it is not flat. Vibration is the problem.
Colin
Gordon W22/10/2011 18:13:49
2011 forum posts
I like the homemade fly-cutter, I made something almost identical to use as a trepanning tool with the steel plate to be cut mounted on an angle plate screwed to the cross slide, worked well. I think the extra flywheel effect helps on small lathes. As mentioned Bogstandard has some very good stuff on fly-cutting.
wheeltapper25/10/2011 15:47:11
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424 forum posts
98 photos
Posted by Steve Withnell on 22/10/2011 17:25:39:
I cut the piece dry, so I'll break out the WD40 and see how that works out.
 
The Indian flycutter slot would take a bigger piece of tool steel than 1/4 inch, but not much.
 
 
I had thought taking light cuts I'd get away with it. Clearly not. I was going to set it up in the mill and run a 10mm slot drill through, as I needed much more than 1/2 inch overhang. At that point I thought I might as well make something more solid.With my M&S version I'm going to creep up the depth of cut and see what happens, 1.5mm wasn't bad at all.
 
Roy - did you spot what my piece of scrap was?
 
 
 
 
Hiya Steve.
just remembered this, no I don't , sorry.
blame it on old age.
 
Roy.
Clive Hartland25/10/2011 17:22:58
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2929 forum posts
41 photos
Steve, Looks like a scrap crankcase off a Nemett?
 
Clive
Steve Withnell25/10/2011 18:14:40
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858 forum posts
215 photos
That's it! I think I made two of most things!
 
 
I didn't flycut the crankcase, but used an endmill in 3mm wide cuts, so it has a distinctive machining pattern all over.
 
 

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