Quickly mounting workpiece in chuck to run true
|Chris Heapy||26/04/2013 10:32:35|
|209 forum posts|
I don't know if this is an old trick or not (it probably is - few things are new in this game). Anyway, the job is to mount some bar ends in the chuck for facing, and you want them to run true, but neither end is machined so no reference point.
For this I use the 'bearing on a stick' method shown below. Simply, it is a ball bearing (extracted from a broken computer hard drive) mounted on a suitable length of square section steel, which itself is mounted into a tool holder.
To use: mount the workpiece in the chuck as accurately as you can by eye, do not tighten the chuck firmly - it just needs to be tight enough to hold the piece so it won't move on its own, yet able to be repositioned when the bearing is pressed against it. The photos are self-explanatory (I hope). Spin the workpiece slowly and bring the bearing into contact (which will be intermittant), then continue pressing until it runs true. The sound it makes is as good an indicator as any. Back off the bearing and tighten the chuck more firmly and re-check, if OK tighten fully.
By similar means the bearing trick can also be used to make thin-ish disks run true by pushing it up against it's front face, it just needs mounting along the line of the bed instead of across it.
|65 forum posts|
You're right, it is not a new trick, I have oft seen this device called a "nudger". However, this post is a good reminder that I need to make one, especially as I have just decided to scrap an old printer which will undoubtedly produce the necessary bearing.
543 forum posts
Also works well if you have a chuck which is a bit old and worn centralises the stock very well.
I made a double ended one so it's then easy to change it around on the Aloris QCTP from facing to turning mode.
Took the bearings from an old VCR.
|Ian S C||26/04/2013 12:37:26|
7468 forum posts
Been using one for years, the roller on a "stick" that I use was part of a (I think) lathe steady, got it at a machinery auction at the NZ Railways back in the mid 1980s, when the Govt was selling off anything that wasn't nailed down. I'v seen drawings of similar tools over a hundred years ago, it was in the form of a horizontal Y, the bar runs in the fork. Ian S C
2746 forum posts
You've just reminded me why I kept a reclaimed bearing from my bandsaw repairs,
|Joseph Ramon||26/04/2013 13:46:31|
107 forum posts
A wooden stick with the lower end between the lathe shears, or even a screwdriver can be used to do this with care.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.