How to measure and grind form tool.

[FTlatheworks]

I have been making parts for a very large expensive machine at work. It looks like a mini pulley but it has a smooth radius instead of a v groove. I ground a tool by matching the shape of the part, but I know I didn’t do it correctly because I don’t have much experience. I can grind tools that work, but unless it’s a threading tool, I’m sure my angles and clearances are all off. The parts look and function ok and the tool gets the job done, but it’s by no means cutting efficiently.

My questions are 1. How do you measure a part like this properly?

2. How do you calculate the angles and reliefs for the form tool?

The diameter of the part is only ,595. I made some out of hdpe to test my form tool, then made the rest out of aluminum. I’ve attached pictures below. I will post a picture of my parts (2 in plastic 1 in aluminum) then I will post the form tool and the original steel part.

 

[pontiac428]

I'd measure with a radius gauge set or gauge pins to find the radius for your grind. The angles are the easy part, they're the same reliefs and rakes you'd use (based on the material being cut) on any other lathe tool. Maybe a side rake isn't needed if it's an in-and-out cut, but the back rake and definitely the reliefs come straight out of the book. Hone it sharp and use plenty of cutting fluid.

 

[derf]

Optical comparator is the best way.

 

[pontiac428]

Optical comparator is the best way.

Of course! By that, you mean setting a gauge pin in the groove and holding it up to the light, right?

I wish I could remember which drawer in my toolbox I put the temp controlled room and CMM in...

 

[FTlatheworks]

Optical comparator is the best way.

I wish! There’s a cheap one on fb marketplace right now.

 

[Weldingrod1]

When I needed a precision radius tool I did it on my Quorn. I roughed and ground the clearance with a separate diamond grinder and a CBN pin.

Sent from my SM-S911U using Tapatalk

 

[FTlatheworks]

I'd measure with a radius gauge set or gauge pins to find the radius for your grind. The angles are the easy part, they're the same reliefs and rakes you'd use (based on the material being cut) on any other lathe tool. Maybe a side rake isn't needed if it's an in-and-out cut, but the back rake and definitely the reliefs come straight out of the book. Hone it sharp and use plenty of cutting fluid.

Sounds good. Can I use cheap radius gauges, or do I need a nice set?

 

[pontiac428]

Sounds good. Can I use cheap radius gauges, or do I need a nice set?

Depends on the application and how critical the fit. Calipers might get you close, and then fine tuning the grind on your form tool to match the original will get you there in the end.

 

[FTlatheworks]

Depends on the application and how critical the fit. Calipers might get you close, and then fine tuning the grind on your form tool to match the original will get you there in the end.

I don’t even know how to use radius gauges yet. I’ll pick some up though.

 

[redgrouse]

I have been making parts for a very large expensive machine at work. It looks like a mini pulley but it has a smooth radius instead of a v groove. I ground a tool by matching the shape of the part, but I know I didn’t do it correctly because I don’t have much experience. I can grind tools that work, but unless it’s a threading tool, I’m sure my angles and clearances are all off. The parts look and function ok and the tool gets the job done, but it’s by no means cutting efficiently.

My questions are 1. How do you measure a part like this properly?

2. How do you calculate the angles and reliefs for the form tool?

The diameter of the part is only ,595. I made some out of hdpe to test my form tool, then made the rest out of aluminum. I’ve attached pictures below. I will post a picture of my parts (2 in plastic 1 in aluminum) then I will post the form tool and the original steel part.

Lots of good info but one point I would make is the front clearance is far too much looks approx 45 deg ! it should be around 10/12deg. I appreciate you have stoned a very small area at the cutting point that may well be a smaller angle but I would grind it closer to a standard clearance angle, makes a better and stronger tool.
Also depends on the accuracy required but for many jobs comparison to a good set of radius gauges is just fine, if you need a rad that's not available just drill a hole in a piece sheet metal and cut the hole in half = a rad of you choice.
Hand grinding is an acquired skill and takes practise, a steady hand, well dressed wheel and a good eye, most of my tools are hand ground and back in the 60's it was the norm to grind your own tools unless it was a complex form tool.
A couple of pic's of some of my tools made over the years -