Fun. Love the sin sweep
Homemade Tip Replacement Lathe
- Thread starter nataddrho
- Start date
DeeDeeCues
Well-known member
Im late to this thread but i use those same block bearings for my low rpm finishing lathe, that spins slowly while epoxy hardens.
It looks like your design is good enough, but if you wanted to improve runout you could use a belt and pulley to drive a mandrel that’s fixed in one of your bearings. That would require making a mandrel with a pin that matches your shafts, which would exceed your budget if you don’t have tooling already.
DeeDeeCues
Well-known member
The runout appears to be because he isn't using a bearing on his drive side. It appears he has his chuck mounted directly to a spider coupling.
I missed that. Amazon sells these bearings in packs of 2 so I assumed he had one on both ends of his shaft.
DeeDeeCues
Well-known member
Yeah, I can't figure this one out. The OP seems to have some knowledge, but this would be a perfect project to show what not to do for a lathe spinner. Several people have already commented on how great this looks, so maybe they are taken in by something.
In reality, this is no better, and possibly worse, than one of those spinners that use an electric drill strapped to a board with a bearing on one end. The drill ones at least have a rigid drive that isn't letting the joint end run anywhere it wants.
I'm not trying to be mean, but for anyone who doesn't know, the coupler on the motor is a three-part coupler that is made to be slightly flexible to account for any misalignment between a rigidly mounted motor and the driven end of a rigidly mounted shaft (shaft in the mechanical sense, not cue shaft). These couplers fit together by friction. When they are allowed to run like this, they can walk apart. If that happens while changing a tip, the shaft and chuck (and part of the coupler) will be sent flying.
I encourage people who want to build something like this to see some advice from someone who has worked in machine design.
Engineering is the art of trade-offs. There are many versions of the constraint triangle, but here is a common one:
You can only have two of the three corners of the triangle. From your comment above you aren't willing to sacrifice High Quality, so your only options are to either spend more money building something with higher performance, or taking a long time to optimize something that still has high performance.
For this project I am deliberately picking Low Cost and Done Quickly, so I must live with Low Quality as a constraint. Now that I know this, what is the magnitude of my Low Quality?
I know that a flexible coupling will have run-out, and from the video it looks to be about 1/8". The pillow bearing is mounted about an inch from the tip. Using the rule of small angles, the run-out at the tip is approximately 1/8" x 1"/27" = 0.005" or 5 mils. Lets say the bearing has some additional slop, so that the tip deviates around 10 mil while spinning.
This is unacceptable work-piece run-out for a cutting tool on a carriage.
However, the 10 mil is absorbed by the fact that I am using a wooden block wrapped in sand paper as my tool, and holding it with my hands, which is even worse precision than the runout
EDIT: This is also one of the reasons machine shop guys complain that engineering doesn't know what they hell they are doing, and that this will never work well. There are usually layers of management and finances demanding all three corners of the triangle at once, and engineers need to cut corners to keep schedules working.
You can only have two of the three corners of the triangle. From your comment above you aren't willing to sacrifice High Quality, so your only options are to either spend more money building something with higher performance, or taking a long time to optimize something that still has high performance.
For this project I am deliberately picking Low Cost and Done Quickly, so I must live with Low Quality as a constraint. Now that I know this, what is the magnitude of my Low Quality?
I know that a flexible coupling will have run-out, and from the video it looks to be about 1/8". The pillow bearing is mounted about an inch from the tip. Using the rule of small angles, the run-out at the tip is approximately 1/8" x 1"/27" = 0.005" or 5 mils. Lets say the bearing has some additional slop, so that the tip deviates around 10 mil while spinning.
This is unacceptable work-piece run-out for a cutting tool on a carriage.
However, the 10 mil is absorbed by the fact that I am using a wooden block wrapped in sand paper as my tool, and holding it with my hands, which is even worse precision than the runout
- Compared to ISO 9001 and expected machine shop quality standards, this won't pass.
- Compared to changing a tip completely by hand like in Dr. Dave's videos, it is an improvement.
EDIT: This is also one of the reasons machine shop guys complain that engineering doesn't know what they hell they are doing, and that this will never work well. There are usually layers of management and finances demanding all three corners of the triangle at once, and engineers need to cut corners to keep schedules working.
Last edited:
Results:
Removing old tip
Gluing on new tip and holding in place while cyanoacrylate sets:
New tip:
Sanding, shaping and burnishing tip: (60 grit, 100 grit, 330 grit and leather)
Done:
If you look closely, the sides aren't perfectly flush, but it levels out quickly as I reshape any mushrooming as the tip breaks in.
The whole process took 20 minutes, and was much better than mailing/traveling/downtime to pay someone else to change the tip, and way faster than doing the whole thing by hand without any machines.
Removing old tip
Gluing on new tip and holding in place while cyanoacrylate sets:
New tip:
Sanding, shaping and burnishing tip: (60 grit, 100 grit, 330 grit and leather)
Done:
If you look closely, the sides aren't perfectly flush, but it levels out quickly as I reshape any mushrooming as the tip breaks in.
The whole process took 20 minutes, and was much better than mailing/traveling/downtime to pay someone else to change the tip, and way faster than doing the whole thing by hand without any machines.
I still vividly remember the noises from those things when connecting to the interweb. then finally after 15 minutes you got connected and got the web page up you wanted to see and someone inevitable picked up the phone that was connected on the same line.
Vernier is a word I never use, I always call it a dial caliper or simply a caliper. I am not a machinist even though I have used and own machining equipment. I was doing a welding job at a machining shop, (they are the ones who effed up the parts that I had to fix ironically) I was looking for a "caliper" and there was only one guy in the shop, I asked if he had one. He acted like he didnt know what I was asking for, then he said do you mean a vernier? When I replied yes he handed me a dial caliper. This just happened in the last year.