# Round-nosed lathe tooling?



## Harvey (Jan 7, 2018)

I need to produce some large-radius bends in some 5/16 x .035 4130 tubing and thought I'd do so by cutting some round-bottomed 5/16 wide grooves in one end of my Harbor Freight's sheet metal slip rollers.  However, I can't seem to find any round-nosed lathe tool bits.  Why is that?

Harvey


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## Jimsehr (Jan 7, 2018)

It would take about 5 min to grind one out of high speed steel 
 or carbide.


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## Bob Korves (Jan 7, 2018)

Make your own from HSS.


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## BillWood (Jan 7, 2018)

You could grind your own maybe ? Or use a circular carbide insert ?

Have a google and look up Form tools.

https://www.google.com.au/search?q=...bFxMfYAhWHJ5QKHXu4AyIQ7AkIag&biw=1246&bih=615







 at approx 2:24


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## Dabbler (Jan 8, 2018)

I regrind those cementerd carbide tools for this sort of work.  They don't work well as they come, and they are perfect for the kind of thing you want to do!


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## Harvey (Jan 8, 2018)

Thanks, Guys, for your replies.  I've seen blank tool stock before and always figured that it's intended for cutting custom shapes.  However, I wouldn't think that a simple 5/32rad would be uncommon.  Also, making something "by eye" doesn't seem (at least to me) to follow the machinist's "code of perfection".  

Can a tool blank be formed with a "common" bench grinder or belt sander? The tool doesn't need to be perfect but I don't want to end up with something crappy either.

Harvey


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## Glenn Brooks (Jan 8, 2018)

Harvey,  yes, use a bench grinder and medium to fine wheel.  A belt sander probably won’t give you enough control to properly shape the tool.  Lots of videos and instructional threads on grinding HSS tooling out there.  Just as in grinding drill bits, takes a bit of practice to make the correct shape.  But it’s not a big deal to learn. Use a set of concave radius gauges to control the shape.

Glenn


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## rgray (Jan 8, 2018)

Use a radius gauge. Compare your grind to the gauge to see your progress in making the tool.
No radius gauge? Poor man's/emergency 5/32 radius gauge...drill a 5/16 hole in some sheet metal and cut the hole in half.
Now you have a gauge.


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## mikey (Jan 8, 2018)

If I were to grind a round nose tool, I would use HSS and use a radius gauge like @rgray said. I would mark the top of the blank with a Sharpie and scribe a line to define the shape and then grind it on a belt sander. In my opinion, a belt sander is the ideal tool for lathe tool grinding. Set the tool rest at 12 degrees to give you adequate relief so the tool cuts instead of rubbing and hone the top to remove any burrs.

Use a slow speed and feed manually. This tool will have a LOT of surface contact and will chatter if you go too fast.


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## Harvey (Jan 8, 2018)

Thanks Guys!

Harvey


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## benmychree (Jan 8, 2018)

mikey said:


> If I were to grind a round nose tool, I would use HSS and use a radius gauge like @rgray said. I would mark the top of the blank with a Sharpie and scribe a line to define the shape and then grind it on a belt sander. In my opinion, a belt sander is the ideal tool for lathe tool grinding. Set the tool rest at 12 degrees to give you adequate relief so the tool cuts instead of rubbing and hone the top to remove any burrs.
> 
> Use a slow speed and feed manually. This tool will have a LOT of surface contact and will chatter if you go too fast.


12 degrees is quite excessive and would result in a weak cutting edge; 5 deg. would be more than enough, unless you were using Armstrong style tool holders, in that case, it would not be enough.


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## mikey (Jan 8, 2018)

benmychree said:


> 12 degrees is quite excessive and would result in a weak cutting edge; 5 deg. would be more than enough, unless you were using Armstrong style tool holders, in that case, it would not be enough.



A matter of opinion, perhaps.


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## benmychree (Jan 8, 2018)

mikey said:


> A matter of opinion, perhaps.





mikey said:


> A matter of opinion, perhaps.


No, a matter of fact; I speak with over 50 years working at the trade.


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## mikey (Jan 8, 2018)

I certainly don't have that kind of experience in the trade but I do have an interest in HSS tool grinding. It has been sort of a pet focus for me for the last 30 years but I grant that I am not in a production environment. Still, I've ground a bunch of form tools over the years and have found that 12 degrees works well on a round nose tool like this (as opposed to the 8-10 degrees that is normally recommended). If the nose radius was narrower, I would increase the relief angles to 15 degrees to lower cutting forces even more to reduce chatter potential and improve finishes. 

As I said, a matter of opinion.


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## Dabbler (Jan 8, 2018)

hey, we all do what works of us.  A matter of how you use it as much as how it is made!


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## pds65 (Oct 14, 2018)

I was looking for inserts like this and Kennametal has some inserts, also micro100 has half and full convex radius bits, too but @ $40 for something I can grind from HSS blanks, I think I'll try that first too as Jimsehr mentioned above


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## petertha (Oct 14, 2018)

I'm going to be faced with this exact same situation making steel rollers for a mini tubing bender. It will see both imperial & metric tubing +/- their particular OD tolerances. From what I've read, a good finish & dimensional accuracy on the radius groove is somewhat important. The other issues (depending on the bender design) is not just making one roller wheel, it may have to be a matched set.

I've had moderately decent luck making simple hardened parts out of O1 tool steel just using torch & (oven) tempering. If I turned a dedicated cutter disc looking profile from O1 tool steel, I could make the appropriate cutting diameter + relief angle + hold-down hole in one turning operation. Or maybe even get fancy & also turn an edge relief on the upper lip. That just leaves a tool holder which could be a blank of steel, tapered on the business end & threaded hole for fastener. I'm not sure I would trust it to make the entire groove in one plunge operation if it large-ish radii, but the groove could be roughed out with parting tool & this tool reserved for final finishing.

General idea sketch shows a 0.375" cutter disc x 3/16" thickness with 6-32 button head bolt. I'm not sure how far you could scale it down before the fastener gets too tiny. At that point I guess break out the cutter grinder machine LOL


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## Bob Korves (Oct 14, 2018)

petertha said:


> I'm going to be faced with this exact same situation making steel rollers for a mini tubing bender. It will see both imperial & metric tubing +/- their particular OD tolerances. From what I've read, a good finish & dimensional accuracy on the radius groove is somewhat important. The other issues (depending on the bender design) is not just making one roller wheel, it may have to be a matched set.
> 
> I've had moderately decent luck making simple hardened parts out of O1 tool steel just using torch & (oven) tempering. If I turned a dedicated cutter disc looking profile from O1 tool steel, I could make the appropriate cutting diameter + relief angle + hold-down hole in one turning operation. Or maybe even get fancy & also turn an edge relief on the upper lip. That just leaves a tool holder which could be a blank of steel, tapered on the business end & threaded hole for fastener. I'm not sure I would trust it to make the entire groove in one plunge operation if it large-ish radii, but the groove could be roughed out with parting tool & this tool reserved for final finishing.
> 
> General idea sketch shows a 0.375" cutter disc x 3/16" thickness with 6-32 button head bolt. I'm not sure how far you could scale it down before the fastener gets too tiny. At that point I guess break out the cutter grinder machine LOL


That tool looks like a likely chatter producer on steel due to the large radius.  Find or make one that is really rigid, and then mount it as rigidly as possible.


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## petertha (Oct 14, 2018)

That's what I suspect/fear too Bob. The commercial tool I have with round carbide insert has a milled pocket. I thought about adding that recess feature on tool holder but I'm not really sure how much the that might be contributing to stabilizing the cutter. It might have more to do with cutting edge repeatability? My only experience with this tool is making the valves on my radial engine. It was also roughed out & then the circular cutting tool made the final tulip shape. But the difference is I could creep in on it so minimized all that lip contact which is where chatter rears its ugly head. 

I thought about a mini Radii cutter which is a way better way of making these profiles... but not at these small diameters.


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## T Bredehoft (Oct 14, 2018)

NO one has addressed the difficult part of the cut. removing most of the material. 

Use a cut off tool to remove 80% of the metal


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## petertha (Oct 14, 2018)

Post #17 above ^^ _but the groove could be roughed out with parting tool & this tool reserved for final finishing ^^_

Actually I've used a X,Y step-over technique on a few occasions to obtain accurate curved profiles. Its helpful (necessary?) to have the (depth, travel) table worked out beforehand. That's another option for this radius groove question depending on accuracy - depth cut in increments, blue the stair steps, file contour to finished form.


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## Dabbler (Oct 14, 2018)

Peter, the main difference between your sketch and the button tool you showed in the picture is that the carbide tool is ground to be positive rake.  This takes much less pressure and helps eliminate chatter.  Nice work on the stepover!

A suggestion is to make your roughing cuts using a carbide or HSS tool with a manageable radius, the do final cleanup using a button tool.  OR you can just live with an accurate cut using conventional tools and then polish for finish.

- my toolmaker friend keeps saying that "there always more ways to do a job than toolmakers in the room" (!!)


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## petertha (Oct 15, 2018)

Good point. No reason why rake couldn't be cut into the top face of tool steel button when the other features are being turned.


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## Dabbler (Oct 15, 2018)

Peter how about making it out of a 1/2 in HSS blank, with a holder to hold it?  Longer tool life than O1...

You lose the ability to rotate the cutter... Hmm makes me wonder if HSS is available in a through-hole round stock.


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## Nogoingback (Oct 15, 2018)

I know that most guys probably don't own one, but the Eccentric Engineering Diamond Toolholder
can be used with round HSS steel blanks up to 1/4" diameter.  Haven't tried it yet, but I might 
after reading this thread.


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## NortonDommi (Oct 15, 2018)

Hi *Nogoingback*,
                             I have left & right hand Diamond Tool Holders and love them I use 16 mm tools and have clamps for 6 mm-1/4" & 8 mm - 5/16" and use square bits for most turning and round  when I want a nice radius.  Very fast to change tool bits and set height.
 Another way would be to drill a hole in the end of a bar and slot the bar then drill and tap for a clamp screw.  Turn a  radius on the end of a bit of tool steel the diameter wanted,(old drill bit shank),grind to the center and fit to hole in bar.  This works surprisingly well and can be made from scrap.


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## Nogoingback (Oct 15, 2018)

I do have a right hand Diamond tool holder that I sometimes use, and have had good results with.  After writing this last night,
I thought of digging out an old HSS drill bit and cutting off the shank for a tool.  Cheaper than ordering stock from Travers.

Not sure I followed you on the drilled and slotted bar.  Do you have a pic?


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## Jimsehr (Oct 15, 2018)

I went out and ground a .312 wide radius tool and cut a few grooves in a piece of steel today to see if it would cut without first roughing it out. 
I did it on a 11 inch Logan with no problems. Got a good finish with no chatter. I will post a pic when I can. Tool made out of HSS with some top rake.


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## petertha (Oct 15, 2018)

Nogoingback said:


> Eccentric Engineering Diamond Toolholder
> can be used with round HSS steel blanks up to 1/4" diameter..



Interesting. I've heard that too but I don't see a picture of that round HSS/carbide blank configuration on their website. Does the holder have a Vee notch & the rod gets clamped in there like the square bit? Happen to have a pic of that?
https://www.eccentricengineering.com.au/index.php?option=com_content&view=featured&Itemid=101

Also, just being picky - wouldn't the projected round section cut an ellipse due to the rod's back angle clearance & probably exaggerated a bit more with any positive rake on the upper surface?

The issue with any of these 'hold the cutter' type ideas (including mine) is that the cutting profile may well have penetrate half its diameter which means the supporting tool holder doesn't have very much meat to grab onto or support without interfering with the cut profile itself. Maybe one could braze the button on like a conventional turning tool, but now its getting even more complicated. A tool & cutter grinder would make an accurate radius shape with all the requisite relief geometry directly out of HSS blank, but not everyone has such a machine.

For larger grooves the weapon of choice is a Holdridge Radii principle, but I think the smallest arc is maybe .75" or so


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## petertha (Oct 15, 2018)

I've made profile cutters out of HSS. Nothing fancy but I thing correctly ground, finished, very sharp etc. They worked 'ok' in aluminum. But at a certain contact circumference then start to plow vs cut efficiently. In this example (~ 0.9" hemi combustion chamber) I then decided to make a mini Radii cutter & the cutting difference was like night & day. Feed-sweep-feed-sweep, done in no time with no fuss. I think extending this operation to steel, especially tough stuff like what tubing rollers would be made of, might be a bit more challenging yet. The problem is, this radii principle just doesn't scale well to small arc diameters.


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## Dabbler (Oct 15, 2018)

Form tooling needs a very rigid setup to work well (for example braze-on radii cutters).  Your small radii cutter idea is fantastic!  Really nice Work!


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## Nogoingback (Oct 15, 2018)

petertha said:


> Interesting. I've heard that too but I don't see a picture of that round HSS/carbide blank configuration on their website. Does the holder have a Vee notch & the rod gets clamped in there like the square bit? Happen to have a pic of that?
> https://www.eccentricengineering.com.au/index.php?option=com_content&view=featured&Itemid=101
> 
> Also, just being picky - wouldn't the projected round section cut an ellipse due to the rod's back angle clearance & probably exaggerated a bit more with any positive rake on the upper surface?
> ...




The holder has V notches on two sides, so a round would be clamped between them.  




Not sure, but I don't think it would cut an ellipse because the OD of the rod is still a circle (looking down along it's axis).  Also, the tool is presented
to the work at an angle which cancels out some of the angle ground into the tool.  But, you're right, there is a limit to how far into the
material the tool could cut before interference with the holder.  That depends to some degree on how far out of the holder the tool
is extended, as well as the diameter of the tool.  But after all, these holders probably weren't really designed for serious profiling: the fact that
they can be used that way is just a bit of a bonus.  I suspect that chatter would be a limiting factor, at least in the smaller
size tools.  

What is Holdridge Radii principle?


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## petertha (Oct 16, 2018)

Holdridge has produced a lathe accessory for many years. I just called it that because some people are familiar with the brand name. There are several home-brew versions. I guess a better description would be radius cutting principle. If the cutting bit is inside the swing axis, it cuts a ball/spherical shape on spinning stock. If the bit is outside the swing axis, it cuts an internal circular groove. Those are the highlighted skinnier cylindrical looking tool holders in pic.

http://www.holdridgemfg.com/


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## petertha (Oct 16, 2018)

_Not sure, but I don't think it would cut an ellipse because the OD of the rod is still a circle (looking down along it's axis). Also, the tool is presented
to the work at an angle which cancels out some of the angle ground into the tool.  _

The way I see it, if the circular section cutting tool rod is positioned at an angle in the toolholder like post#29 pic to provide back clearance & fed into the work on the spindle rotation axis, that is equivalent to cutting a section across a cylinder & looking down on it from that cut plane...which yields an ellipse. This shows an example 15-deg angle & resultant effect on dimensions. To help visualize consider if the tool angle was greatly exaggerated like at 45 deg and now cut across the horizontal plane. The width would always equal the tool diameter but the profile would not be semi-circular, it grows into a longer aspect ratio elipse. And I suspect positive rake exaggerates this even more. Whether this is dimensionally significant or not is up to the machinist. Probably not on small diameter grooves. I'm just pointing out the geometry.


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## petertha (Oct 16, 2018)

_Form tooling needs a very rigid setup to work well (for example braze-on radii cutters). Your small radii cutter idea is fantastic! Really nice Work! _

Thank you. 
I suspect another issue is the flame brazing temperature relative to hardened O1 might be hot enough to re-anneal it. Carbides survive the heat but that does us no good if we cant make a carbide profile. Silver soldering? Sounds like a PITA. You see this is why I mentally justify a tool & cutter grinder! LOL


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## Dabbler (Oct 16, 2018)

And a very nice one your tool and die grinder is!  I've made some form tools using silver soldered carbide, and they work well.  I get some chatter when the cutting area gets pretty wide, but I clean that up with wet and dry...

- Nothing like the accuracy required for your valves, for instance....


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## Jimsehr (Oct 17, 2018)

Pic of tool and steel bar.https://photos.app.goo.gl/ct54fraDnrXSPo9L9

This is a pic showing what a full .312 wide radius hand ground tool looks like and what the steel bar looks like with the groove formed in it. Took about 1/2 hour to  make using a 11 inch Logan to do it.


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## Nogoingback (Oct 17, 2018)

petertha said:


> _Not sure, but I don't think it would cut an ellipse because the OD of the rod is still a circle (looking down along it's axis). Also, the tool is presented
> to the work at an angle which cancels out some of the angle ground into the tool.  _
> 
> The way I see it, if the circular section cutting tool rod is positioned at an angle in the toolholder like post#29 pic to provide back clearance & fed into the work on the spindle rotation axis, that is equivalent to cutting a section across a cylinder & looking down on it from that cut plane...which yields an ellipse. This shows an example 15-deg angle & resultant effect on dimensions. To help visualize consider if the tool angle was greatly exaggerated like at 45 deg and now cut across the horizontal plane. The width would always equal the tool diameter but the profile would not be semi-circular, it grows into a longer aspect ratio elipse. And I suspect positive rake exaggerates this even more. Whether this is dimensionally significant or not is up to the machinist. Probably not on small diameter grooves. I'm just pointing out the geometry.




I  see what you mean, though as you say, probably not all that significant.  Any one that plans on an accurate profile would
pick a different tool I imagine.


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## Doubleeboy (Oct 18, 2018)

mikey said:


> I certainly don't have that kind of experience in the trade but I do have an interest in HSS tool grinding. It has been sort of a pet focus for me for the last 30 years but I grant that I am not in a production environment. Still, I've ground a bunch of form tools over the years and have found that 12 degrees works well on a round nose tool like this (as opposed to the 8-10 degrees that is normally recommended). If the nose radius was narrower, I would increase the relief angles to 15 degrees to lower cutting forces even more to reduce chatter potential and improve finishes.
> 
> As I said, a matter of opinion.



I am with Mike on this.  In my time grinding form tools from HSS or hi carbon steel blanks I like 10 to 15 degrees relief.  Lowers cutting forces, reduces chatter in my experience.  If I had 20 hp, flood coolant I might think different but for home shop size lathes like my 10EE going with more relief makes life easier.


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## Nogoingback (Nov 4, 2018)

As a follow up to this post, I decided that I would try the diamond tool holder with round piece of HSS and see what results
I could get.  The tool was an old drill bit of unknown quality (probably Chinesium) with piece of mystery steel round bar.
Eccentric Engineering suggested using the same jig they supply for grinding square tools, so I did that.  The jig grinds
a lot of rake into the tool, but the tool holder is angled and cancels that out some.  The best measurement I could take showed
a net rake of 13 degrees.  

An initial cut with a regular lathe tool showed that the steel machined easily.  The first pass with the round tool produced 
chatter, but slowing the spindle speed fixed it.  I was able to cut some grooves pretty easily by rotating the tool so that it
produce a slight shearing cut, but beyond a certain depth the feed force required increased and cutting pretty much stopped.
I also had problems with the cutting edge breaking down fairly quickly.  I imagine a better piece of tool steel and a bit less
rake might have helped with that.  Rotating the tool in the holder so that it was "square" to the work (no shearing) didn't 
work at all.  

So, with a better tool and some more experimenting I think this could be made to work, though not for deep or accurate
grooves.


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## mikey (Nov 4, 2018)

In the past, I've noticed that form tools do not like a lot of rake. The broad area of engagement allows a thin work piece to climb onto the tool, creating chatter. That led me to use anywhere from zero to 5 degrees of back rake and to make sure the tool was dead on center height; this worked better, for me anyway.


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## MarkM (Nov 4, 2018)

If you want to do this with some sort of accuracy and make it manageable with little chatter is to use chords.  There is a formula in the Machinery handbook.  It has neen awhile but I had a job that required a large radius on a disk and this is how I went about it.  Your basically making steps cutting equal depths on both side of the rad. Then work your way in to calculated depths and then leave .010 on final depth then blend in only to max depth.


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## Nogoingback (Nov 4, 2018)

mikey said:


> In the past, I've noticed that form tools do not like a lot of rake. The broad area of engagement allows a thin work piece to climb onto the tool, creating chatter. That led me to use anywhere from zero to 5 degrees of back rake and to make sure the tool was dead on center height; this worked better, for me anyway.




Thanks Mikey.  Yeh, I figured there was too much rake since the the thin cutting edge was breaking down pretty quickly.  When I 
get a chance I'll regrind and try again.  I was careful about making sure the tool was on center so I don't think that was a factor.


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## Nogoingback (Nov 4, 2018)

MarkM said:


> If you want to do this with some sort of accuracy and make it manageable with little chatter is to use chords.  There is a formula in the Machinery handbook.  It has neen awhile but I had a job that required a large radius on a disk and this is how I went about it.  Your basically making steps cutting equal depths on both side of the rad. Then work your way in to calculated depths and then leave .010 on final depth then blend in only to max depth.




Thanks Mark.  I can look that up in Machinery handbook and give it a try.


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## MarkM (Nov 5, 2018)

I made two form tools with rads.  One as to size and the other had a slighly smaller rad.  I free handed and blended the radius with the first tool then went to final size by plunging the proper radius tool to proper depth.   Use a parting blade to make your steps.


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