paul
Member
Posts: 8
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Post by paul on Jul 9, 2007 10:49:35 GMT
What is the best way to mark out two perpendicular lines on the end of a circular bar (less than 1" in diameter)? The centre position is marked so scribing through that gives one line but how to scribe another at right angles to it? (The lines need to be full diameters not just radii, i.e I want to end up with a 'cross' on the end of the bar).
And! How could I scribe a third line parallel to one of the above?
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Post by havoc on Jul 9, 2007 11:01:17 GMT
Using a V block might help. You put the bar in a V block. Use a square to scribe the first line. Turn the V block on its side (or bolt it to an angle plate) and scribe the second line.
Scribing 2 parallel lines goes fine if you use a "height scriber" (one of those things where a scriber sits on a vertical bar). Scribe the first line, lower or raise as needed, scribe the second line. Those lines are scribed parallel with the reference plane.
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Post by Tel on Jul 9, 2007 11:02:28 GMT
You'd do best with a pair of vee blocks and a height gauge. Set the gauge to the centre height of the bar - draw it across to scribe a horizontal line on the end of the bar, now turn the bar untill the line is vertical - use a square for this - and strike your second line. The parellel lines can be got by then adjusting the height gauge (once or a 'undred times if you need that many)
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Post by dickdastardly40 on Jul 9, 2007 11:08:38 GMT
Paul,
A couple of methods spring to mind, I don't know exactly what equipment you have so please bear with me:
Use a surface plate, vee block, surface guage (scriber block) and engineers square. Set the already scribed line vertical with the square against the surface plate and the scriber at centre height.
If you have turned the diameter with a 4 jaw, set one jaw of the chuck a known and repeatable distance from the lathe bed, scribe using the tool in the post at centre height to give the first line. rotate the 4 jaw 1/4 rev and set the same distance from the bed. First line should now be perpendicular and you can scribe the second as before using the tool. If the jaws are not evenly spaced, ie you've turned from an odd shape or have used a 3 jaw, you can set the first line vertical using a square setting from the saddle before you scribe the second.
On the first method raise the scriber to mark the third line, in the second raise the tool or set a scribing block on the saddle of the lathe to mark the horizontal lines.
As ever hope this helps
Al
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paul
Member
Posts: 8
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Post by paul on Jul 9, 2007 19:59:49 GMT
Thanks Havoc... Tel... & DD.
Seems like another liberal application of spondulix is required - boy those surface plates are expensive!
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Post by jgb7573 on Jul 9, 2007 20:24:05 GMT
Get yourself a sheet of plate glass. That's plenty good enough. Depending on how accurate you need this to be, you could even use a piece of kitchen worktop. They're pretty flat.
Have fun,
John
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Jul 9, 2007 21:47:06 GMT
G'day Paul.
I use a marble floor tile which I got for AU$10.00.
Regards, Ian
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Post by dickdastardly40 on Jul 10, 2007 5:24:32 GMT
Paul,
Dependant on the size of your lathe saddle, that will likely be flat enough, ground and smooth to use as a surface plate for your needs.
Al
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Post by havoc on Jul 10, 2007 10:11:52 GMT
I use a piece of ground flooring like Ian. A leftover from the rebuild. If you really need the precision of a ground surface plate, then it is time to think about keeping everything at the same temperature. Or redesign...
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Post by ilvaporista on Jul 10, 2007 12:27:24 GMT
Offcuts from a stonemason are also cheap. Over here kitchens have real marble worktops and the offcut from cut outs for sinks etc. are sold very reasonably.
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Post by mackintosh on Jul 10, 2007 16:20:46 GMT
I got a 2ft square surface plate off flea bay for a tenner. Very heavy but so useful. If you go to road steam images there is some photos of my engine on said surface plate. I just cover it with a smear of oil and a wooden cover and don't have any rust issues. Bob
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