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WIP Steel grinder disk machining
- Thread starter Nathan the Machinist
- Start date
Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
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Okay, let me get back to this WIP thread. This is where I left off:
They were heat treated, rough machined, welded and tempered.
The next step is the most important one. I'm setting up to cut the working face, OD, and then single point bore the ID all in the same setup. Making these cuts without moving anything virtually eliminates any runout on the important surfaces. This is the key to this disk.
Here's the setup, holding it by the outer edge:
And the finished cut:
The bore is .6252 nominal with a total tolerance of about half a thou.
At this point all the precision machining is complete, but I still need to cut the back bevel. I'll need to hold onto the stub to do this, and as you'll recall that stub is just welded onto the disk. Although the bore was single pointed after welding, the OD of the stub was not. So I held it by the OD of the disk with the finish machined face against the chuck and skimmed the diameter of the stub to have a more accurate surface to hold onto for the final turning op.
This will allow me to cut the back bevel with better accuracy. Although the accuracy of the bevel is not that important, if it is off by a lot it will effect the balance. I am balancing these, but it needs to be fairly close to start with and accurate geometry helps.
Next I mount a disk by that stub and turn the back bevel:
I'm done turning it. All that is left is to balance it, broach the keyway and test in on a motor.
Edit:
Being a disk rather than something like a shaft it is pretty straight forward to balance. There are a number of different approaches to this, the technique I'm using is commonly used for balancing things like grinding wheels. It is slow but accurate.
This is a technique that any of you can use to balance things like contact wheels, grinding wheels etc. If it is fundamentally a disk shape, this will work.
To start I need a flat level surface. I'm sitting a small granite surface plate onto the table of an old small bed mill that is stable and already relatively level. The level is a master precision level with graduations of 50 millionths per inch. They're not too spendy and most machine shops keep one around for measuring and straightening bow and twist from things like lathes. (aside: a "level" lathe isn't necessarily level, it is straight, and you can measure that with a few measurements from a precision level). A sheet of aluminum foil is about half a thou and can be used as a shim to get the plate good and level. With practice this only takes a few minutes.
Once the plate is level you need to level a set of blades. I'm using ground precision thin parallels here, but anything that is thin, smooth and precision ground flat will work. First I shim out any twist by measuring level from one end to the other in a series of measurements designed to find the low corners and shim them up.
Then I get the "blades" extremely level front to back.
My balancing setup is level within a couple tenths. With practice you can set this up to this degree of accuracy in about 30 min.
...more later...
They were heat treated, rough machined, welded and tempered.
The next step is the most important one. I'm setting up to cut the working face, OD, and then single point bore the ID all in the same setup. Making these cuts without moving anything virtually eliminates any runout on the important surfaces. This is the key to this disk.
Here's the setup, holding it by the outer edge:
And the finished cut:
The bore is .6252 nominal with a total tolerance of about half a thou.
At this point all the precision machining is complete, but I still need to cut the back bevel. I'll need to hold onto the stub to do this, and as you'll recall that stub is just welded onto the disk. Although the bore was single pointed after welding, the OD of the stub was not. So I held it by the OD of the disk with the finish machined face against the chuck and skimmed the diameter of the stub to have a more accurate surface to hold onto for the final turning op.
This will allow me to cut the back bevel with better accuracy. Although the accuracy of the bevel is not that important, if it is off by a lot it will effect the balance. I am balancing these, but it needs to be fairly close to start with and accurate geometry helps.
Next I mount a disk by that stub and turn the back bevel:
I'm done turning it. All that is left is to balance it, broach the keyway and test in on a motor.
Edit:
Being a disk rather than something like a shaft it is pretty straight forward to balance. There are a number of different approaches to this, the technique I'm using is commonly used for balancing things like grinding wheels. It is slow but accurate.
This is a technique that any of you can use to balance things like contact wheels, grinding wheels etc. If it is fundamentally a disk shape, this will work.
To start I need a flat level surface. I'm sitting a small granite surface plate onto the table of an old small bed mill that is stable and already relatively level. The level is a master precision level with graduations of 50 millionths per inch. They're not too spendy and most machine shops keep one around for measuring and straightening bow and twist from things like lathes. (aside: a "level" lathe isn't necessarily level, it is straight, and you can measure that with a few measurements from a precision level). A sheet of aluminum foil is about half a thou and can be used as a shim to get the plate good and level. With practice this only takes a few minutes.
Once the plate is level you need to level a set of blades. I'm using ground precision thin parallels here, but anything that is thin, smooth and precision ground flat will work. First I shim out any twist by measuring level from one end to the other in a series of measurements designed to find the low corners and shim them up.
Then I get the "blades" extremely level front to back.
My balancing setup is level within a couple tenths. With practice you can set this up to this degree of accuracy in about 30 min.
...more later...
Nathan the Machinist
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This works on the principle that the heaviest side wants to be on the bottom. It's that simple. However, this is not like hanging a lawnmower blade on a nail to balance it after sharpening, you want much greater accuracy than that. So simply putting the disk on a nail or shaft and letting the heavy side find bottom is far too insensitive, as is mounting it onto bearings or something similar, there's simply too much drag.
This is done by running an extremely straight, hardened and finely ground shaft through the bore and letting things rest on the very level, very smooth thin ground parallels. There is very little drag or friction or bias of any type and the heavy side will repeatably find the bottom with this setup to within a few thousandths of a ounce. In order for this to work your setup needs to be finely finished and everything needs to be straight and level with no dirt, dents or other imperfections that would cause things to hang up.
So I let everything sit until it stops moving. This takes a few minutes. Once it has settled down I mark the high side with a sharpy. Then I start adding weights to it. I start with my "large" weights which weigh 3/4 of a gram until I find the mass that flips the disk around.
I have a drill mounted in a Bridgeport and I've set the stop on the quill so it drills a hole that removes an equivalent amount of steel as the weight of one weight. So, if a disk needed 5 weights to come around I drill four holes. Then it goes back onto the balancing setup for a finer adjustment. This time with weights that weigh .19 grams.
I repeat the process until it is level enough that a .19 gram weight will pull it around to the bottom regardless of where that weight is added which tells me I'm balanced within 30 thousandths of an ounce inch.
The balancing could be taken finer still, but let's be honest, most folks aren't going to be running these on ABEC7 super precision bearings, and any little amount of runout you have on the spindle in your motor that shifts the axis of the disk away from the axis of rotation is going to affect your balance more than this.
Balancing like this is a slow iterative process, which is going to be a bottle neck in releasing these, so I'll probably do a weekly release of only a few at a time. Please be patient while I process these.
The next step is broaching
Broaching is not rocket science.
I'm balancing before broaching because the material removed in broaching is similar to the material added by the key. The key is generally slightly less, but there is also the added weight of the little set screws, which I think makes it a wash given the small random variations there will be from one person's setup to the next. Given how close these are to the center of rotation the effect is not that great regardless. I tried it both ways and experimented with adding small weights on the same side of and opposite to the key and found that balancing before broach worked a little better.
Here's the finished final disk:
The last thing I do is spin it up on an unmounted motor and let it coast down. The motor is unrestrained so any vibration or other troubles would have an opportunity to show up here. Video if you're curious:
[video=youtube_share;-b_h7NaZxKg]http://youtu.be/-b_h7NaZxKg[/video]
And that completes this WIP.
This project was done at the request of the folks here on this forum. The purpose of this thread was to both illustrate the machining process and also to generate some awareness of the project so that folks would be aware of it when it was finished. So this thread was part documentary and part advertisement. I'd like to extend my gratitude to the folks on this forum for allowing this thread, as I am well aware it is blurring that line between legitimate WIP and overt sales. It is not my intent to spam this forum. With that in mind please refrain from discussing costs and availability or anything else that would be construed as "commerce" and save those questions for the sale thread which I will post in the appropriate area. I'll bump this thread with a link when it is ready.
Other than discussing sales I invite discussion!
Thanks for following along.
This is done by running an extremely straight, hardened and finely ground shaft through the bore and letting things rest on the very level, very smooth thin ground parallels. There is very little drag or friction or bias of any type and the heavy side will repeatably find the bottom with this setup to within a few thousandths of a ounce. In order for this to work your setup needs to be finely finished and everything needs to be straight and level with no dirt, dents or other imperfections that would cause things to hang up.
So I let everything sit until it stops moving. This takes a few minutes. Once it has settled down I mark the high side with a sharpy. Then I start adding weights to it. I start with my "large" weights which weigh 3/4 of a gram until I find the mass that flips the disk around.
I have a drill mounted in a Bridgeport and I've set the stop on the quill so it drills a hole that removes an equivalent amount of steel as the weight of one weight. So, if a disk needed 5 weights to come around I drill four holes. Then it goes back onto the balancing setup for a finer adjustment. This time with weights that weigh .19 grams.
I repeat the process until it is level enough that a .19 gram weight will pull it around to the bottom regardless of where that weight is added which tells me I'm balanced within 30 thousandths of an ounce inch.
The balancing could be taken finer still, but let's be honest, most folks aren't going to be running these on ABEC7 super precision bearings, and any little amount of runout you have on the spindle in your motor that shifts the axis of the disk away from the axis of rotation is going to affect your balance more than this.
Balancing like this is a slow iterative process, which is going to be a bottle neck in releasing these, so I'll probably do a weekly release of only a few at a time. Please be patient while I process these.
The next step is broaching
Broaching is not rocket science.
I'm balancing before broaching because the material removed in broaching is similar to the material added by the key. The key is generally slightly less, but there is also the added weight of the little set screws, which I think makes it a wash given the small random variations there will be from one person's setup to the next. Given how close these are to the center of rotation the effect is not that great regardless. I tried it both ways and experimented with adding small weights on the same side of and opposite to the key and found that balancing before broach worked a little better.
Here's the finished final disk:
The last thing I do is spin it up on an unmounted motor and let it coast down. The motor is unrestrained so any vibration or other troubles would have an opportunity to show up here. Video if you're curious:
[video=youtube_share;-b_h7NaZxKg]http://youtu.be/-b_h7NaZxKg[/video]
And that completes this WIP.
This project was done at the request of the folks here on this forum. The purpose of this thread was to both illustrate the machining process and also to generate some awareness of the project so that folks would be aware of it when it was finished. So this thread was part documentary and part advertisement. I'd like to extend my gratitude to the folks on this forum for allowing this thread, as I am well aware it is blurring that line between legitimate WIP and overt sales. It is not my intent to spam this forum. With that in mind please refrain from discussing costs and availability or anything else that would be construed as "commerce" and save those questions for the sale thread which I will post in the appropriate area. I'll bump this thread with a link when it is ready.
Other than discussing sales I invite discussion!
Thanks for following along.
Last edited:
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Great thread Nathan! Normally I have to head to CNCZone to get my machining fix!
I love seeing how someone with skill and experience can bring such quality to a 'simple' product. I hope one day to have the skills and machinery to tackle a project this well. My benchtop mill and lathe are jealous!
I love seeing how someone with skill and experience can bring such quality to a 'simple' product. I hope one day to have the skills and machinery to tackle a project this well. My benchtop mill and lathe are jealous!
Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
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Okay, a few of these are finished and I've gone ahead and started a sale thread in the appropriate area : http://www.bladeforums.com/forums/showthread.php/1106998-Steel-grinding-disks
Thanks,
Nathan
Thanks,
Nathan
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Nathan
Thanks for the process photos and expaoinations
I'm interested in the balancing process.
If you would video what you're doing when you do a balancing I'd really appreciate that.
Your explanation is good, but that type of movement and "feel" would really come across in a video.
Thanks for the process photos and expaoinations
I'm interested in the balancing process.
If you would video what you're doing when you do a balancing I'd really appreciate that.
Your explanation is good, but that type of movement and "feel" would really come across in a video.
Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
Moderator
Knifemaker / Craftsman / Service Provider
- Joined
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Balancing a steel disk, video by request (12345678910)
[video=youtube_share;6eQIBZ9ICCo]http://youtu.be/6eQIBZ9ICCo[/video]
I was asked to post video of how I accurately balance a precision machined steel weldment. This video is dull folks. Very dull. Like watching paint dry. I made this video and even I can't watch it...
This kind of balancing starts by leveling thin hard precision ground blades into a nearly perfect plane that is perfectly level. I used a master precision level calibrated with divisions of 50 millionths per inch and .0005 thick aluminum foil as shims. This is very level. There is a finely finished precision ground hardened steel shaft run through the disk. When this shaft with the disk on it is sit on the blades it is free to turn with extremely low drag. So the heavy side will find the bottom with a high degree of accuracy.
All of this happens very very slowly. Hence the painfully tedious video. Over all I think the entire process takes about an hour because I leave it alone and go do something else while it sorts out. Thus I'm only doing a couple per day.
At first the disk settles down. Then I add weights to the top of the disk. At first I use larger weights that weigh 3/4 of a gram. I add one weight and confirm it is not enough. Then I add another. Then another. With the third weight I have crossed the tipping point. So I drill out two shallow holes that are equivalent to the two weights and start the process over again with finer weights.
The finer weights weigh .185 grams, which is about .0065 ounces. The first little weight is not enough. The second it too much. So I drill a shallow hole ( not more than a dill point) equivalent to one little weight and sit the disk on the beams once again and let it settle out. Once it is settled I add a small weight at the top and let the disk come around and settle down one last time as a final check. That small weight was enough to pull the disk all the way around to the bottom. At .0065 ounce at about 4" from the center of rotation that weight, in theory, can not exert more than 26 thousandths of an ounce inch of torque. So, considering margins for error, it is probably pretty safe to say it is balanced to better than .030" ounce inch, which is fine for the application.
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Awesome Thanks.
This is gold.
This is gold.
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I have one now, and it is A-W-E-S-O-M-E!!! 
:thumbup:
It's my favorite color too... shiny!
I think instead of mounting it to a motor, I'm going to hang it from the shop ceiling as a beautiful art installation.
:thumbup:It's my favorite color too... shiny!
I think instead of mounting it to a motor, I'm going to hang it from the shop ceiling as a beautiful art installation.
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I have one now, and it is A-W-E-S-O-M-E!!!
It's my favorite color too... shiny!
I think instead of mounting it to a motor, I'm going to hang it from the shop ceiling as a beautiful art installation.
I agree,but just wait till you run it.Man Oh Man it is sweet.
Stan
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Nathan- I really enjoy your wip threads. It's always a pleasure seeing a master at his craft. Thanks for taking the time to post this.
Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
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Thank you guys, I appreciate the accolades.
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I think instead of mounting it to a motor, I'm going to hang it from the shop ceiling as a beautiful art installation.
I received mine yesterday evening; I had the same thoughts Nick. There are photos of the weld on Facebook and Instagram. Unfortunately my aloomineum disc is pretty dinged up so it will need to be used.
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Nathan, or whomever can contribute, what would be the ideal setup for this disk in order to achieve its maximum potential and reduce the chance for runout? From what has been posted, removing the motor and using an arbor such as the AR17 that Bladsmth posted, would decrease/ eliminate runout. But, how would one set up the motor and arbor? Are there any examples (pictures) of the ideal setup for those of us who are not as "mechanically," inclined.
I know this is asking for a lot but after attempting quite a few google searches, I've come empty handed and thought it more prudent to ask a real machinist anyway.
Thanks in advance.
I know this is asking for a lot but after attempting quite a few google searches, I've come empty handed and thought it more prudent to ask a real machinist anyway.
Thanks in advance.
