# Simple workholding fixture



## dparker (Dec 25, 2007)

Hello All: I hope you all had a Merry Christmas with friends and family! 
Here is a simple mounting fixture for holding something with a center hole. On the lathe it might be a flywheel for a motor that needs just a little more work. I believe I saw this several years ago in HSM and used it to finish one of my engine's flywheels.
Turn a piece of scrap to a diameter that would be a snug fit in the bore, and then measure the diameter of a roll pin or roller bearing needle and file or mill a flat just slightly deeper on the fixture diameter just slightly longer than the pin. Slide the "flywheel" over the shaft and then slip the roll pin in the open space and wring the part in the direction that will tighten the roll pin to resist the torque of the cutting tool. With the pin parallel with the bore the part will accept quite a good amount of torque and is easily removed when done machining the part. A shoulder could be used on the fixture to help resist the part moving down the shaft if desired.
For these pictures I used a oilite bearing because it was handy but still should show the idea. I would think light cuts would be in order here, this has helped me in the past and I will most likely use it again--fast and easy. 















I hope this helps somebody as I have not seen this mentioned anywhere I have read for several years.
Don, Now have a Happy and Healthy New Year!


----------



## tattoomike68 (Dec 26, 2007)

Thanks thats a good trick to remember. That can be made a little different to make a one way clutch too.


----------



## deere_x475guy (Dec 26, 2007)

Hey great tip thanks for sharing.


----------



## dparker (Dec 26, 2007)

Tatoomike: Would the "clutch" be in only removing about 1/2 of the flat spot leaving a edge high enough to prevent the roller moving to the other side and into a locking position? I had never thought of this but it could be a useful tidbit to use in a pinch. No pun intended,--- well maybe.
Don


----------



## tattoomike68 (Dec 26, 2007)

dparker  said:
			
		

> Tatoomike: Would the "clutch" be in only removing about 1/2 of the flat spot leaving a edge high enough to prevent the roller moving to the other side and into a locking position? I had never thought of this but it could be a useful tidbit to use in a pinch. No pun intended,--- well maybe.
> Don



Nothing more than a radius and a little larger flat would make it a one way clutch. one way it spins free the other it grabs. the working part can be on the female or male part.

It was in an Ingenious mechanisms book. I have seen it used on machines too.


----------



## Hilmar (Dec 26, 2007)

This has been used by Wood Turners for centuries. We use it to look on a bowl blank to turn. But wood is a different story, it locks the pin in. On metal I would not use it to turn a flywheel since it will not lock and the wheel will spin free. On small parts as you show it may be OK. So be care full on a larger Part.
Hilmar


----------



## Powder keg (Dec 27, 2007)

This was featured in one of the Machinist Bedside readers. I have used it on flywheels and have had good luck with it. It locks up extremely good for what it is. Yet, you can loosen it by turning it backwards with your hand. I like using it as an arbor to polish parts in the lathe. You can hold items buy the bore and not mar the surface like a chuck will. I built a flywheel for Phillip Duclos fire eater. The whole thing was turned on an arbor like this:O) I have several different sizes in my toolbox.


----------



## 1Kenny (Dec 27, 2007)

If you didn't want to leave tool marks on a part I think this would be a good tool to use. I believe the term for this tool is a Dog Clutch . I have seen this used with starters on some aircraft engines.

Kenny


----------



## Cedge (Dec 27, 2007)

Mike is right about the clutch idea. For those who remember LeChatNoir's funky people powered "Contraption" from the thread at http://www.homemodelenginemachinist.com/index.php?topic=435.msg2600#msg2600 , the drive mechanism used this exact clutch design to couple the hand crank power source to the belt drive. He invited me to visit his build log, sometime back, and I was amazed at the ingenuity and simplicity of the design.

Steve


----------

