Drawing A Straigt Line Over A Length Of Bar Stock

grepper

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I am machining a new handle for the compound slide on my lathe. I hate the tiny little handle that comes with it. Every time I turn it another layer of knuckle epidermis is removed, and the handle part is fixed to the cross piece that bolts onto the screw. So I’m making a new, longer one with thrust washers in the handle for smooth and knuckle bashing free operation.

I need to drill two holes in the handle cross bar, (1) for the bolt for the handle, and (2) for the hole for the bolt to attach it to the compound screw. I don’t have a X/Y table for my drill press, so I need to draw a line straight down the side of the cross bar so the holes are perfectly aligned.

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Seems simple, but it proved more difficult that I thought. How to hold a ruler against the surface and know it goes perfectly from center to center down the length of a bar? If it’s off just a little… I know, I could put a protractor on each end… But one end is rounded, making that method difficult. I could try to carefully measure it – problematic.

It’s night here, and I was sitting on the couch next to my wife while she watched some used episode of Criminal Minds. The living room was mostly dark, save for a light on a table at the end of the couch. So I was sitting there holding the part pictured here, scratching my head and puzzling over how I could accurately draw the line, when I noticed something.

Did you see it too?

So, I shined a flashlight down the length from one end. Bet you see it now!

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The orientation of the light does not matter. As the light is moved, it just moves the reflection around the circumference of the bar. Of course the reflection is still perfectly straight down the length of the bar.

Anyway, it’s a super quick way to get a perfectly straight line down the side of reflective bar stock. I thought it was cool.

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True it is cool and well observed by your good self. :encourage: I would most likely have popped the part in the lathe chuck, plonked some texta near where I wanted the cross holes to be then with a tool set on center height scribed a short mark where the holes were to be. Later, (after both horizontal lines are marked.) a slight twist of the part with the tool just touching should make a verticle mark at the centre of the holes. But hey, your way worked, congrats. :cheerful:
 
Thank you! I knew there must be some super easy way to do that. I have not had a lathe long, and that did not occur to me. Duh! :rolleyes: I guess if were camping or trying to do it on something that couldn't be chucked up in a lathe the flashlight idea might come in handy. I must add, you sir, are most magnanimous.:)
 
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I stick it in a vise and run a ruler down it (holding it level) scratching a line end to end
 
The rest of us would rather buy a 2000# milling machine to do that job, slower and with more fiddling around. Great idea!
 
And it even drops right on the QCTP! I can see where that would be very handy to have around.
 
To recall someone's question posed a couple of weeks ago, that's also a very good application for the use of a surface gauge....

-frank
 
I've run into that dilemma once in a while, and used a small piece of channel. Actually it was a "C" channel shelf bracket that is 1/2" x 1/2". Lay it on the shaft and it will center itself.
 
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