Oh boy, I did it again! PRAZI SD400.

[WobblyHand]

I decided to start by remaking the bent pinion shaft. Im making it out of A2 tool steel as it can be easily hardened which will make it more rigid and ensure a longer service life as it wont wear when hardened.

Isn't the rigidity of steel practically the same for all grades and compositions? Like under 5% variation? I was told that if one wanted a stiffer boring bar, one needed to change the material, like using carbide, because all the steels were the same.

Nice work. It's hard for me to tell, are you using a parting blade?

 

[SouthernChap]

Good read, as always mate.

Just clarify though, did you say you're using a centre drill as an ersatz chamfering tool on your mill? If so, that's a handy little idea, which is a new one to me.

 

[RaisedByWolves]

Isn't the rigidity of steel practically the same for all grades and compositions? Like under 5% variation? I was told that if one wanted a stiffer boring bar, one needed to change the material, like using carbide, because all the steels were the same.

Nice work. It's hard for me to tell, are you using a parting blade?

I’ve read this, but only through this site and I view much of what I read on the internet with a wary eye. In the raw state this may be true, but you harden tool steel for a reason.

When you harden a selected type of steel for a job, you do that with the job it will have to do in mind and harden then temper or draw back to the hardness level that will get you the best overall performance.

Take a quality 3/8” round bar of tool steel and anneal it. You can now bend it like a pretzel.

Take that same type snd size and harden it and it will shatter like glass, dangerously so if you attempt to bend it or cause it to be impacted as in a charpy test.

charpy test at DuckDuckGo

DuckDuckGo. Privacy, Simplified.

duckduckgo.com

Take the same steel again, harden it and draw it back to 50-55RC and you have something stiffer than the material in its raw state, that will still give quite a bit before deforming, that also now has a high degree of wear resistance.

Good read, as always mate.

Just clarify though, did you say you're using a centre drill as an ersatz chamfering tool on your mill? If so, that's a handy little idea, which is a new one to me.

Had to think on that a bit, but yeah, worked great. Counter sinks can also be employed and you can get many different “angle/taper mills” going down that road.

 

[WobblyHand]

But the Young's modulus of various steels are nearly identical. Perhaps that's the incorrect metric to use? Is there a better metric?

According to AmesWeb, Young's modulus of Steel article, the stiffness of steels maybe varies by 10% or so. They have a list of many steels and their Young's modulus. https://amesweb.info/Materials/Youngs-Modulus-of-Steel.aspx A2 has a YM of 207 GPa, A36 is 200 GPa. Not a heck of a lot different (3.5% stiffer). O1 is 214 GPa.

I understand that tool steel has favorable properties, and there are some very good reasons to use it, just trying to understand this rigidity thing.

 

[RaisedByWolves]

But the Young's modulus of various steels are nearly identical. Perhaps that's the incorrect metric to use? Is there a better metric?

According to AmesWeb, Young's modulus of Steel article, the stiffness of steels maybe varies by 10% or so. They have a list of many steels and their Young's modulus. https://amesweb.info/Materials/Youngs-Modulus-of-Steel.aspx A2 has a YM of 207 GPa, A36 is 200 GPa. Not a heck of a lot different (3.5% stiffer). O1 is 214 GPa.

I understand that tool steel has favorable properties, and there are some very good reasons to use it, just trying to understand this rigidity thing.

I’ve tried looking into this after reading about it here and have read everything from it matters/does not matter to it stiffens it a little but not enough to matter, so I only have my experience to go by.

What I know is that harder materials will shatter rather than bend and take a set like a softer steel of the same type. That I can prove with a simple test, and whatever minutiae academics want to argue over is not a concern of mine.

I just want what I know works.

We have a special part we used in one of our legacy does that we would wear out, crush or otherwise destroy on a regular basis.

The company that made these went out of business and I was tasked with making a supply of these in house. We went through a couple dozen of these a year so I made about 30pcs out of the amount of material I was given.


These were made out of A2 and hardened and drawn back to ~45 RC. Picture a hollow T shape 2.5” tall with a 1” body and 1.5” flange on the open end. This gets a shoulder bolt inside and a spring on the outside that is captured by a thin threaded washer.

The bolt goes in, the spring goes on and the washer threads onto the stripper bolt (that had to be modified too) to make a compact self contained spring pack that then threaded onto the machine to do its job.

Now, I told you all that to tell you this.


I made these 6yrs ago and out of the 30 or so I made none of the parts I made have been deformed or worn appreciably, and 26 are still in serviceable condition.

We did lose some due to catastrophic mishaps, but the majority of them were rebuilt several times and some are still on their first build.


So I’m more prone do what I know works in a given situation.


As to O1 being inherently stiffer, I can agree with that without even looking it up, it’s pretty tough.

I didn’t want to use it in this application as it needs to be oil quenched (hence the O designation) which would warp it and require grinding straight for use.

With A2 I can just bring it to a .0005 oversize and polish it after hardening.

 

[WobblyHand]

I’ve tried looking into this after reading about it here and have read everything from it matters/does not matter to it stiffens it a little but not enough to matter, so I only have my experience to go by.

What I know is that harder materials will shatter rather than bend and take a set like a softer steel of the same type. That I can prove with a simple test and whatever minutiae academics want to argue over is not a concern of mine.

I just want what I know works.

We have a special part we used in one of our legacy does that we would wear out, crush or otherwise destroy on a regular basis.

The company that made these went out of business and I was tasked with making a supply of these in house. We went through a couple dozen of these a year so I made about 30sec out of the material I was given.


These were made out of A2 and hardened and drawn back to ~45 RC. Picture a hollow T shape 2.5” tall with a 1” body and 1.5” flange on the open end. This gets a shoulder bolt inside and a spring on the outside that is captured by a thin threaded washer.

The bolt goes in, the spring goes on and the washer threads onto the stripper bolt (that had to be modified too) to make a compact self contained spring pack that then threaded onto the machine and did its job.

Now, I told you all that to tell you this.


I made these 6yrs ago and out of the 30 or so I made none of the parts I made have been deformed or worn appreciably, and 26 are still in serviceable condition.

We did lose some due to catastrophic mishaps, but the majority of them were rebuilt several times and some are still on their first build.


So I’m more prone do what I know works in a given situation.


As to O1 being inherently stiffer, I can agree with that without even looking it up, it’s pretty tough.

I didn’t want to use it in this application as it needs to be oil quenched (hence the O designation) which would warp it and require grinding straight for use.

I wasn't doubting your use of the material, nor your experience. I was, however, questioning "stiffness" of materials, but from a narrow point of view. There are other important properties, which you have clearly stated above, that are good reasons for using tool steel. If tool steel "just works" for the application, measured by longevity, just can't argue with that reality. Wish I had access to heat treating capability, but that is lacking in my home shop.

Excellent work, by the way. Enjoying your thread on bringing your Prazi's back to life. Sorry for the interruption.

 

[RaisedByWolves]

I wasn't doubting your use of the material, nor your experience. I was, however, questioning "stiffness" of materials, but from a narrow point of view. There are other important properties, which you have clearly stated above, that are good reasons for using tool steel. If tool steel "just works" for the application, measured by longevity, just can't argue with that reality. Wish I had access to heat treating capability, but that is lacking in my home shop.

Excellent work, by the way. Enjoying your thread on bringing your Prazi's back to life. Sorry for the interruption.

No your good, I appreciate the conversation.

I’m always willing to help and with the complexity of the subject matter there will always be unanswered questions and differences of opinion.

You want fun, watch two knowledginel toolmakers argue over the “proper “ way to do something.

Thanks for the kind words.

 

[durableoreo]

From what I read, the springiness of steel does not change much with alloy or heat treatment. If you heat treat it, it will resist permanent deformation but its Young's modulus is not changed.

Seem opposite of my experience but maybe it's because when I bend a thin piece of steel it is deforming elastically and yielding at the same time. But if it's heat treated as a spring, the yielding behavior is minimized and the elastic behavior is isolated.

The elastic behavior of steel has to do with the matrix of iron atoms and their connection to each other. If you bend a steel bar a little, it will snap back because there is some "give" in the connection between iron atoms. If you bend it more, the iron atoms will slip past each other. The organization doesn't change but the iron atoms have new neighbors.

When you heat treat a steel, impurities break up the iron matrix into regions of iron with boulders of carbon-iron complexes between them . How that makes steel seem less able to bend is a little mysterious. Somehow there is less opportunity for slippage when the iron matrix is broken up. Maybe someone else can explain better...

 

[durableoreo]

Nice work. It's hard for me to tell, are you using a parting blade?

I noticed that tool, also. Maybe we'll get a another glimpse of it in these project threads.

 

[RaisedByWolves]

I noticed that tool, also. Maybe we'll get a another glimpse of it in these project threads.

Nice work. It's hard for me to tell, are you using a parting blade?

Got carried away and forgot to answer this.



I’m failing hard here, just going to link to the thread.

Tips and tricks specific to the Prazi/Hobbymat machines.

Our machines are some of the finest machines ever made in this size or class of machine. In the past there were many competitors, but not all had the rigidity or power of the Prazi/H-Mat, so some specific tooling was created to help beginners deal with these other machines limitations. Im...

www.hobby-machinist.com