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Vertical Centering?

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Hugh Gilhespie30/12/2010 21:10:40
130 forum posts
45 photos
Hi, not sure what to call it, but I am wondering what is a good way to find the highest point on a round piece of work when it's in a rotary table and the RT is set up vertically. In other words the work is sticking out horizontally and I want to drill and tap down into the piece at the highest point aiming at the centre of the work.
 
Sorry if this is totally confusing. Not surprising as I am confused myself so it's not likely to be a clear explanation. I guess this is a fairly common requirement and that there will be various ways of making sure that the hole is exactly on a diametetical line. My set up is on the mill and I do have a DRO so I can use an edge finder to zero the X-axis and then set the distance from the edge I need but I'm not at all sure how to set the table's Y-axis so that I am vertically above the centre of the work.
 
Enough blathering. I hope someone understands!!
 
 
Keith Long30/12/2010 21:47:59
883 forum posts
11 photos
Try the same trick as finding centre height on a lathe with a ruler and the tool tip - put a conical point in the mill/drill chuck and the ruler across the top of the job - only difference the ruler needs to wind up horizontal not vertical
Stewart Hart30/12/2010 22:01:15
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674 forum posts
357 photos
Cheep and chearful way
 
With a bit of bar in the chuck wind it across until you can feal it just start to grab a bit of thin paper, cigaret paper is ideal, zero your DRO than advance yourtable 1/2 the sum of the diameter of the bar and the diameter of your work and as near to dam it you wil be on the centre of your work.
 
Or you can buy a wobler but that another story.
 
Hope this helps
 
Stew
Versaboss30/12/2010 22:06:10
512 forum posts
77 photos

Nothing hinders you to use the edge finder on the side of the round bar. Or: chuck a straight round piece of steel in the spindle and touch the side of the bar (cigarette paper test). Then add the 2 radii and move this distance.

Almost as long-winded as your description of what is usually called cross-drilling. 

Happy New Year, Hansrudolf

John Olsen30/12/2010 22:09:44
1294 forum posts
108 photos
1 articles
You can use an edge finder on the cylindrical face. There is a potential problem if the edge finder has a ball end and is not set on the centre height of the job. One way around this is to use an edge finder with a cylindrical end on it.
 
Another way, if you only have an edge finder with a ball end, is to edge find off both sides, noting the reading on the DRO when you do. Then the centre of the job will be halfway between the two settings. This could also be done from the dial, but it is hard to eliminate the backlash error since you have to wind the opposite way when edge finding off the opposite face.
 
regards
John
Terryd31/12/2010 00:19:27
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1946 forum posts
179 photos
hi Hugh,
 
As Keith says the simplest way is to lay a 6" rule across the bar, I use a centre drill in the chuck, set approx in centre, align the point of the drill along the bar and trap the rule gently.  Move the table until the rule is horizontal, then you are on centre.
 
How to check for horizontal?  align with a known horizontal, perhaps a parallel or 2 across the machine bed, a spirit level behind it, or you could even use one of those builders laser levels that are so cheap now or even just do it by eye, depends how accurate you need it .  It is surprisingly accurate and no maths.

Terry

Edited By Terryd on 31/12/2010 00:22:16

Hugh Gilhespie31/12/2010 08:44:58
130 forum posts
45 photos
Thanks to all for the advice. I will probably go with Hansrudolf's method using some silver steel rod in the chuck, I can't use my edge finder as the diameter of the work, 50 mm, means that I can't get the sliding tip close enough to touch the circumference. I wouldn't normally be so fussy and would be happy using the ruler method but the piece is an eccentric strap and the will be fitted with a 200 mm long valve actuating rod so I am keen that the far end of the rod ends up in something close to the right position.
 
Happy New Year to everyone.
 
Regards, Hugh 
Eric Cox31/12/2010 09:29:14
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557 forum posts
38 photos
When you add the two radii together don't forget to include the thickness of the paper
Stub Mandrel07/01/2011 18:27:10
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4318 forum posts
291 photos
1 articles		If you take a tiny skim across the top of the bar with a small endmill, you will create a tiny flat dead on top. Centre and drill in the middle of the flat.

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