Re: Precision level needed or not?

Rogan Creswick
 

Guy, Thanks for the details!

Could you share some pictures / diagrams of the jig you described for scraping? I need to do some inspection (and probably repair) work on a light 10k bed, and I imagine I'll need to make some tooling to help with that.

Thanks!
--Rogan

On Thu, Jun 13, 2019 at 9:01 PM carbure2003 <guycad@...> wrote:
Be careful with this method, you don’t know if your tailstock is aligned, or if it is worn enough to be slightly off axial alignment. In addition, you would have to consider wear on the bed.

Levelling with precision level is my preferred option. Other unknown thing is bed top of v way condition.If there are dints, it may impact levelling.
I rebuilt a few south bend lathes.  In the bed restauration process, the first thing I usually do is the re conditioning of 3 levelling positions: under the headstock first, then tailstock end at the bolt location, and the third one is under the chuck area. Usually, bedways are not damaged under the headstock and have minimum wear at the tailstock end. The zone near the headstock receives many dints, chucks being dropped, stock hitting bedways, etc...  I spend time with a fine honing stone in order to ensure I have identical readings at the 3 locations. Accurate levelling is done with a jig that I manufactured as a template for slide ways scraping. Instead of using top bed ways surfaces, it uses the v profile of bed ways as reference. I level the lathe bed with a master precision level, then I hone my flat surfaces at the reference levelling positions until I get identical readings on the level. When the lathe is back together, the reference under the chuck is used at the same time as the tailstock reference point.

Chienese manufacture master precision levels sold for less than $100. 0.0002" / 10”.  They will  do the job. In between times I need the level, they go out of calibration very easy. I always have to recalibrate mine. My Starrett bought later on Kijiji keeps its calibration quite good.  I have seen level vials for sale on ebay for less than $40. One was mounted in an aluminium holder.  This would enable you to manufacture your own master precision level.
Remember that a lathe does not need to be perfectly levelled, you need to have the twist taken off. A  lathe in a ship is never levelled. It is set properly when ship is in dry dock.

Guy Cadrin

---------- Original Message ----------
From: "Steven H via Groups.Io" <stevesmachining=aol.com@groups.io>
To: SouthBendLathe@groups.io
Subject: Re: [SouthBendLathe] Precision level needed or not?
Date: Thu, 13 Jun 2019 23:08:55 -0400

What you are describing - an alignment bar placed between centers - is one way of checking and setting the tailstock alignment both horizontally and vertically. These alignment bars are commercially available - Edge Technology makes one that is 12” long. Don’t know if such an item could be used to check for lathe bed twist, but if the idea would work, the bar should be max length the lathe can hold between centers.

Steve Haskell


> On Jun 13, 2019, at 9:32 PM, Stephen Bartlett via Groups.Io <tower.op=verizon.net@groups.io> wrote:
>
> I like the plumb bob idea, but have a question.e bed
>
> I have never done this but would it work to put a mandrel known to be the same diameter at both ends on centers and then indicate the surface at the two ends with an indicator on the carriage set at one end and then the other?
>
> At the very least it might be quicker than taking cuts and adjusting twist until the ends are the same?
>
> Steve Bartlett
>
>
>



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