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Need to know best way to machine a chamfer READ

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Mutt

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#1
Hey y'all, I have a piece of cast iron tubing. It's 1/8" wall, 1.1/4" diameter, has a 3/8" wide x 1 1/2" long slot machined into it. I need to know the most efficient way to do a nice looking, heavy chamfer on the outside of the slot. The chamfer should extend to the bottom edge of the slot and the top of the slot will measure 1/2" wide when finished. Cosmetic appearance is a must. What's y'all's thoughts on this matter?
 

BaronJ

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#2
Hi Mutt,

I would dig out my carbide wood router bits and select one suitable for the chamfer you want. Use it as though it was a HSS cutter but a little slower.
Go steady because you want to avoid the cutter chipping and leaving a score line.
 

Mutt

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#3
I'm looking for something like what would be equal to a 1º first cut, 2º second cut a 3º final cut. What I am not understanding is if the center line of the slot is vertical in my mill, will the entire slot get cut all in one pass, including the ends of the slot . 3/8" wide

Here is the unaltered slot
slota.jpg

here is what I need to achieve
slotb.jpg
 

JimDawson

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#4
What I am not understanding is if the center line of the slot is vertical in my mill, will the entire slot get cut all in one pass, including the ends of the slot . 3/8" wide
It will if you use the correct cutter. But the included angle is about 53 degrees, which is not a standard cutter. Because you are cutting on an arc, the ends of the slot will be cut a bit deeper than the sides in a strictly straight cut at constant depth.

If you don't have a 5 (6?) axis CNC mill, a little hand work with a file(s) and some emery cloth will probably be required.
 

Mutt

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#5
Isn't a 45º included a standard size ? I can live with that. So what would the resulting slot look like if you just machine it in a straight line using a router bit in the mill? The straight sides will be fine I know, but what happens to the 3/8" radius at each end of the slot?
 

BaronJ

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#6
Hi Mutt, Guys,

That would depend upon whether you cut both sides of the slot at the same time ! Not advised !
I would use the whole of the depth of the cutter to do the ends and then each edge separately. That way you will also avoid climb milling.
If you are careful you won't have to do any blending in.
 

JimDawson

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#7
Yes, a 45° included angle is standard.

The chamfer will be a bit wider at the ends. It will cut about 0.046 deeper into the OD than on the sides. This is due to the height of the arc segment relative to the sides.
 

Mutt

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#8
Ok. Thanks. I will machine a few test pipes and experiment before actually attempting the real part
 

RJSakowski

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#9
Here is what your chamfered slot will look like. 1`-1`/4" OD, 1`/8" wall, 3/8" slot, 45º chamfer, 1/2" wide at top. Pipe Slot.JPG Pipe Slot 2.JPG
 

RJSakowski

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#10
Note in the above post that the chamfer doesn't go to the bottom of the slot. You would need to go .047" deeper with the chamfer. If you do so it will be .564" wide at the top.
 

Mutt

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#11
cool. So will it look the same if I use a 4 flute 1/2" ball mill on the ends and a 45º cutter for the sides?
 

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#12
cool. So will it look the same if I use a 4 flute 1/2" ball mill on the ends and a 45º cutter for the sides?
No, the shape would be much different with a ball end mill because it's an arc, not a straight line like a chamfer cutter.

If you have a CNC mill, then you could use a ball end mill and profile the shape as a 3D profile and it would come out correct.
 

Mutt

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#13
Ok, check this out. I got a brand new USA made 4 flute 1/2" ball nose endmill in the mail this afternoon. So I grabbed up a piece of DOM from the scrap pile and milled a 3/8" slot in it followed by the 1/2" ball mill. I can definately live with that. I should have went about .020" deeper and it would be exactly .500 wide.

Thanks y'all

Mutt
DSC01487.JPG
 
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