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Drill running off course

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Eric Cox17/09/2019 09:59:55
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I have just drilled a 2.6mm hole through a piece of gunmetal 5/8" long on the drill press. The drill ran of course and exited the metal off centre. How do I stop it running off centre.

Andrew Johnston17/09/2019 10:10:41
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How far off is it? Is the starting face perpendicular to the drill? In general:

1. Don't use the drill press, especially if it's a cheap one. Use a lathe or vertical mill and machine vice instead.

2. What is the provenence of the drill, cheap or branded?

Andrew

jason udall17/09/2019 10:19:01
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I would add.

Drill chuck run out and straitness

Though 2 .5 is not silly small(try 0.3 mm) the tool holding is critical. 0.1 run out on a 10 mm drill is sort of acceptable it's far too big on a 2.5 mm drill

And typical drill press chucks aren't made to hold small drills well. Plus what rpm. I doubt you are spinning the drill any thing like the 10's of thousands of rpm "ideal".

JasonB17/09/2019 10:19:08
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Was the Punch mark absolutely dead in line with the drill spindle? Assuming it was punched first. Even if a thou or two out at the start it will bend the drill over at an angle so error gets worse the deeper you go.

fizzy17/09/2019 11:18:48
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If I need total accuracy I have found it essential to use a centre drill to start and have the job clamped solid. You need a good centre pop too.

Kiwi Bloke17/09/2019 12:09:58
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I wish the 'tradition' of using centre drills to start drilled holes would die. Centre drills are for making centres - that's why they have the little bit on the end - the bit that breaks off easily. Spotting drills are robust and stiff and make good drill-starting dimples. One with a 90 degree point angle can pre-countersink or chamfer the hole too (if it's going to be less than the spotting drill's diameter). Try to get one without a chisel-edge, i.e. four-facet grind, and you don't need a centre-pop (which is a bit of a problem if you're working to co-ordinates...).

Philip Burley17/09/2019 12:18:27
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I had this trouble drill bronze , A friend re sharpened my drills and since I have had no problems , Some of the new 2.5 mm drills were very poorly sharpened , but they were cheapo ones

regards Phil

JA17/09/2019 12:20:18
785 forum posts
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Eric

You are not alone.

I have experienced a drill running off course with bronze. The drill diameter (all this is from memory) was about 5mm and after a depth of about 35mm the drill was around 2mm off course. The drill was good and dressed to cut bronze. The drilling was done in a lathe and started from a centre drilled hole. The Jacobs chuck was not removed between the use of the two drills. The tail stock alignment is within 0.001". The speed may have been slightly slow. Neat cutting oil would have been used. The bronze was phosphor-bronze bar.

As far as my "lesson learnt log" - this is to be expected when drilling bronzes.

I would ask questions about the bronze bar, like do you really expect it to be perfectly homogeneous?

JA

Kiwi Bloke17/09/2019 12:30:48
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Had to have a rant about misuse of centre drills... Now, back to Eric's question.

Hopefully, all the good advice that has been given will result in success. However, it hasn't been mentioned that if swarf is packing in the hole, horrible things can be expected to happen. Are you trying to drill the hole in one pass, or are you 'pecking', i.e. very frequent complete withdrawal of the bit from the hole, to clear swarf? With a drill that size, you will need to peck every few seconds. It's tedious...

3404617/09/2019 12:31:40
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I must admit to using a centre to spot the hole, not a punch, also I spot both ends and drill halfway through from each.

Bill

Ian P17/09/2019 13:10:45
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If using the drilling machine for small holes (less than about 5mm) that need to be deep and square I do not clamp the job to the table. Regardless of how the drill is started once a decent dimple is created I peck very frequently whilst at the same time rotating the job about one third of a turn for each peck. With the drilI rotating pecking it down will 'jolt' the dimple and the workpiece to centralise it as long as it is only loosely held. I have found that doing this every peck will average out the centering error even if the drill is not running dead true.

The table on my Fobco is pretty square to the chuck axis but even a table had a slight tilt, rotating the job frequently about half a turn will compensate to a large extent.

The smaller the drill the less it will be able to bump the job into position unless the workpiece is very light in weight which rules out using a drill vice to hold the job.

Ian P

Mick B117/09/2019 13:55:20
1182 forum posts
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Posted by Kiwi Bloke on 17/09/2019 12:09:58:

I wish the 'tradition' of using centre drills to start drilled holes would die. Centre drills are for making centres - that's why they have the little bit on the end - the bit that breaks off easily. Spotting drills are robust and stiff and make good drill-starting dimples. One with a 90 degree point angle can pre-countersink or chamfer the hole too (if it's going to be less than the spotting drill's diameter). Try to get one without a chisel-edge, i.e. four-facet grind, and you don't need a centre-pop (which is a bit of a problem if you're working to co-ordinates...).

Do spotting drills cut on the flute land as well as the lip?

I don't know because I've never seen one - they're simply not stocked, or at least not prominently displayed, by model engineering, tooling or DIY shops.

Centre drills cut on the flutes as well as the point, which is why you get a more-or-less truly concentric cut. They also provide piloting guidance to a larger followup drill until the cylindrical land of such a drill is engaged. You can use the pilot as a tiny slot drill, which I sometimes do. Centre drills are stiff, cheap and available. I've broken centre drill pilots, it's true - 3 in the last 15 years, and one of those was a poor-quality example.

I'd probably welcome spotting drills if I could find them as easily, but it looks to me as if you need a bigger range of sizes than the 3 centre drills I regularly use, and they're comparatively dear.

JasonB17/09/2019 14:14:09
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I've been using spotting drills for the last 5-6 years and only use my ctr drills for where ctr support is needed of conical holes for pipe fittings. I get away with just two sizes - 1/8" and 3/16" though have just recently bought a 3mm one for the CNC as I only have metric collets for that.

The cut across the whole width of the flute hence why thay can be use das a combined CSK or deburr prior to drilling the actual hole and can stop soft metals raising up around a tapped hole. You don't have to go that deep with them, think like a large 90deg ctr punch for starting drills so long as the "flat" end of a jobber drill fits into the cone shaped recess it won't wander.

Couple of 1/8" HSS ones here, one of the right is my prefered brand with web thinning that means the "flat" end is very small, both cast about £3. Carbide one I bought recently is even more pointed. It was also half the price of a similar size ctr drill from the same supplier.

Not really stocked by ME suppliers though I have suggested it to Ketan a few times but any industrial supplier will have them and all will sell to public,

Edited By JasonB on 17/09/2019 14:16:56

Ian P17/09/2019 14:26:36
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+1 for using spotting drills

In spite of the pointed tip looking very vulnerable I have found they are actually quite robust and stay sharp for a long time, I've not worn one out yet in several years.

Most suppliers just seem to carry the 60 degree ones but other angles are available (Looks like Jason's picture shows a 90 and 120 versions)

Ian P

Neil Wyatt17/09/2019 15:11:48
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Thanks all for inspiring my monthly rant for Ed's Bench.

angry

Neil

Vic17/09/2019 15:19:09
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I agree about the use of spotting drills but do any of you know why they are so long? I’ve been thinking of cutting a couple down to make them even more rigid.

Ian P17/09/2019 15:26:13
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I wish they were longer!

Ian P

JasonB17/09/2019 15:26:24
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Posted by Vic on 17/09/2019 15:19:09:

but do any of you know why they are so long? I’ve been thinking of cutting a couple down to make them even more rigid.

question

Don't think I would be left with much to hold mine by if I shortened them and certainly could not use then when say spot drilling something in a spin indexer. I only use the pointed end of mine so don't by long reach ones. Ctr drills included for comparrison

20190917_152342[1].jpg

 

 

Edited By JasonB on 17/09/2019 15:27:27

JasonB17/09/2019 15:28:57
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Ian, try some long ones

Ian P17/09/2019 15:41:24
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The slocumb bits in your picture both look to be longer than ones I usually see, I have some very long centre drills which are useful occassionally but I have seen some of the larger sizes 3/8" / 10mm or so where the flutes from either ends would run into each other except for the fact that they are rotated 90 degrees. They might be rigid but dont seem designed for gripping in a drill chuck.

Ian P

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