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How to drill really really really accurately?


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miles&Jules
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How to drill really really really accurately?

Hi Guys..this is actually not a robot question but I guess it relates to robot building techniques, especially for ant weights I guess.

i've been drilling some aluminium for ball joints for our puppets and find it nearly impossible to drill holes accurately in multiples. I've got a centre drill and a set of vernier callipers for measuring.

I'm drilling into 10mm wide lengths of aluminium. So I measure 5mm with callipers then scribe with a razor blade. This is centre then I draw across 5mm from the end.

Then I put the centre drill in the bench drill and line it all up perfectly and then i drill but its .......never perfectly centre. for some reason the centre drill must be moving around. Then i drill the hole with a regular 2.5mm drill bit. It often looks centre but then when I measure its always never perfectly centre

Is there a cheat for this a method that would make this work easily for hundreds of drill holes?

Thanks
Miles
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Post Sun Mar 20, 2011 10:43 pm 
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Glen
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Howdy,

Quick tip for the marking out, dont bother with the scribe. just set your calipers to 5mm and use the hardened jaws of the calipers to do the scribing, hold one end of the jaws on the edge of the work and the other jaw to scribe the line. much faster Smile

What drill press is it? if its a cheapy little $100 deal theres not all that much you can do. the quill (shaft that goes up and down the chuck mounts too) is just wobbly and the chuck isnt accurate at all. On my old ryobi you can literally see it doesnt run true.

The inaccuracy is probably just a compound of quill/chuck free play (wobbly) and having to reclamp the work each time + quality of the vice.

Accurately center punching the holes is probably all you can do if thats the case.

Only cheat i can think of is to make an accurate template out of steel and use this to get the holes in the right place in the aluminium bits. I do this alot for my robots cause im lazy Laughing That is assuming your making lots of the same piece of course

Post Sun Mar 20, 2011 10:57 pm 
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miles&Jules
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Hi Glen
Thanks for the tips Ill give that a go. The drill presses i've got are cheapies (a ryobi and a noname big floor mounted super cheap one. But we have got a bosh drill holder that could be more accurate....ill go and do a test.
thanks again
miles
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Post Sun Mar 20, 2011 11:16 pm 
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miles&Jules
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Hey Just did some drilling using the new "scrapping calliper" technique and then lowered the centre drill onto the aluminium really slowly and it worked...did 3 holes and it looks perfect.....maybe I was just marking the lines inaccurately...Thanks Glen!!!!
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Post Mon Mar 21, 2011 12:05 am 
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Nick
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Glen covered the best tips, but there are some more things yo can do:

Before you scribe the lines, use a felt tip marker pen to black-out the general area to be drilled - I use a really wide tip marker. Let it dry and then scribe the lines - the caliper points will cut thru the marker coating and show you a very bright line that's super easy to see.

You didn't mention centre punching the metal before drilling. Using a sharp punch will help pull the drill on line and also helps you line things up; it is even more important in a drill press that has a loose quill.

Last, you might get better results with a centre drill that has a split point. Its and extra grind that brings the tip of the drill to an actual point, like this:



That stops the drill from wandering and if you centre punch, the drill point will tend to pull itself into the punch mark.

How are you holding the part on the table? Hand holding parts for small holes is OK, but clamping them down is usually more accurate.

Post Mon Mar 21, 2011 6:00 am 
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miles&Jules
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Hi Nick
i will grab a centre punch next time at the hardware. I did have one but it got lost as usual.

Nice idea with the split point on the centre drill. How would I grind that accurately though?

I've got the aluminium mounted on a compound vice bolted to a a pedestal drill. So I can do fine adjustments. The quill seems pretty smooth it doesn't seem to rattle at all...But I will keep an eye on it.

i'll give the black pen a go to thanks for the tips guys!
Miles
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Post Mon Mar 21, 2011 8:15 pm 
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Vignesh



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My dad just uses a large nail or something sharp to use as a center punch. CBF going to hardware shop to get something so perfectly made when you have a nail...
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Post Mon Mar 21, 2011 8:20 pm 
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Nick
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Grinding your own split point drills accurately is something for pros or expensive sharpening machines. You should be able to buy those bits at most Bunnings nowadays - I think the premium range in a purple & black packaging have split points or just ask. Failing that, you could get something on-line from McJing or similar:

http://www.mcjing.com.au/categorybrowser.aspx?categoryid=53 (several sections down the page)

@ Viggy: a nail can work, but a proper punch will work better again. They don't cost much and last for ever. keep it sharp and they are easier to use and more accurate.

Post Mon Mar 21, 2011 10:20 pm 
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miles&Jules
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Hi Nick
So if I punch then use the split point drills I dont even need to use the centre drill?
Thanks

miles
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Post Tue Mar 22, 2011 12:11 am 
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Nick
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Probably not, split point drills work really well for me. The longer and thinner the bits, the more likely they are to wander; I try to buy shorter drill bits when possible, or I cut the shaft down a bit. It sounds like you drill quite a few of these parts so having a dedicated short drill bit would make the operation more efficient.

Post Tue Mar 22, 2011 5:57 am 
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miles&Jules
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Will check em out thanks Nick!
Miles
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Post Tue Mar 22, 2011 6:22 pm 
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