Cutting Radii

[mklotz]

Miniature engines have a lot of rounded-over parts so I built a jig that drops into my mill vise. It's described in detail and pictured here...

https://www.homemadetools.net/forum/rou ... arts-27242

It's served me well over the years and turned out lots of parts. The design was evolutionary so there are no plans but it's not very complicated and there are very few critical dimensions.

[Bill Shields]

alternative for thick parts

drill ream the hole
scribe the radius
put a pin in the hole
clamp the link in a milling vise - pin horizontal sitting on jaw(s)
cut off whatever is needed. Manually rotate the part using the pin as reference - cut off more as needed
belt sand to finish.

[rmac]

Thanks, Bill. This sounds real similar to what pete suggested. I like it!

-- Russell Mac

[shootnride]

This guy did a video a few years ago showing pretty much the method that Pete has described.

https://www.youtube.com/watch?v=hTj6LC6agrg

Ted

[liveaboard]

But if it takes longer than using a rotary table and doesn't work as well as using a rotary table, what's the point?

Unless you don't have a rotary table of course.

It took me some time to make my rounding jig, no doubt a belt sander (as suggested by Harold) would have been faster if I had one.
Or if it's a fairly thin part, just scribe and grind with an angle grinder if your need is merely cosmetic.

[GlennW]

But if it takes longer than using a rotary table and doesn't work as well as using a rotary table, what's the point?

Unless you don't have a rotary table of course.

Exactly what I was thinking!

Looks to me like his method took longer that using a RT to begin with and leaves nowhere as nice a finish.

Not all rotary tables are the same, but mine has a solid plug that screws into the center. I drilled and tapped that plug to accept a 1/4" bolt. For jobs like he showed which don't demand extreme accuracy, I just spin out a quick bushing to fit the hole in the part and bolt it to the RT to center it, add a toe clamp, and make the cut.

[tornitore45]

Two ways I do it, is a potentially dangerous operation but never had a problem by paying attention.

Clamp a pin vertically on the wise, slip a washer/spacer smaller than the radius to cut on the pin, slip the part to cut on the pin
If the part is short have means to lengthen and leverage.
Make sure to conventional mill, never climb or the part can be grabbed.
This is the method I use to cut the ends of connecting rod. Rotation is more than 180 degrees and let you do the fillet between the large head and the smaller shank.
Rotate by hand, take light cuts
Less risk of grabbing by mounting the pin horizontally and cutting with end of the end mill

[Bill Shields]

Less risk of grabbing by mounting the pin horizontally and cutting with end of the end mill

think u r missing the point ->

using the above method with the part clamped in the vise -> nothing is going to move no matter how heavy a cut you take..

clamp cut
unclap rotate
cut
unclamp rotate
cut
repeat

I have also used your 'hand hold turn' method with long parts...but makes me nervous to recommend to someone....

[tornitore45]

I got the point, there are different methods.
Pin horizontal on top of vise to establish reference, part clamped. Turn and clamp yield faceted finish.
Pin horizontal clamped in vise, part free handed, radius above jaws, no need for spacer. Be careful.

We are all aware of the dangers, I did pointed out.

[mklotz]

As I mentioned in my article, the risk of fingers close to a spinning cutter can be ameliorated by attaching a temporary handle to the workpiece. A jeweler's hand vise (not a pin vise) such as this...

https://www.amazon.com/ACE-Hand-Vise-Sm ... CLAMP_VISE

is useful in this capacity.

[tornitore45]

Yap, have one jeweler vise very similar. Very old, very handy, found at a garage sale.