Marking out

This topic has 21 replies, 7 voices, and was last updated 30 April 2011 at 22:13 by Colin Jacobs 1.

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29 April 2011 at 17:03 #67693
Colin Jacobs 1
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@colinjacobs1
Hi been practising with making straight repair plates from 25×75 x3mm BMS that are all the same. The plans call for two holes 12mm from each end and from the edges.

I have engineers blue and scribed the measurements but try as I might the jenny callipers will not equal 12mm from all sides, its about a mil out.

should I just use one side as a datum or do as I have done measured all sides to get the holes central.

I am using the book A Basic Course of Practrical Metalwork by J.R.Bedford if anyone has it. Its great for beginners as it takes u through basic handwork.

MTA.

Colin,
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29 April 2011 at 17:03 #5494
Colin Jacobs 1
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@colinjacobs1
Drill holes
29 April 2011 at 17:12 #67694
Steve Garnett
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@stevegarnett62550
Am I missing something here? If the plates are 25mm wide, and you need a hole 12mm from both sides and the end, then it’s going to be 1mm out anyway in one direction if you get it right in the other two – simply because 12+12=24, not 25. So if the plates are the correct size, then the holes will have to be 12.5mm from the sides, not 12.

And personally I’d use a steel rule to do this, not an odd-leg jenny, which you have to be very careful to keep at right-angles. I’d rather just blue the ends, use a steel rule and scribe lines in appropriate places, I think. One across from each side parallel to the ends, and then either measure to the centre or use normal dividers to find it.

Edited By Steve Garnett on 29/04/2011 17:14:13
29 April 2011 at 17:54 #67697
Colin Jacobs 1
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@colinjacobs1
yes 12.5mm but I thought it would be that all round. it has been a good practical lesson for me and im still learning.
29 April 2011 at 18:04 #67698
Nicholas Farr
Participant
@nicholasfarr14254
Hi Colin, I use one of those 4″ combination type squares for marking out on a typical job like the one you have, and even if you don’t get a line from each side to exactly match up they are normally close enough to dot in between for your holes to be central.

Regards Nick.
29 April 2011 at 18:15 #67700
Steve Garnett
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@stevegarnett62550
Yes there are certainly plenty of ways of doing this. And there’s a good chance that almost any of them is an improvement on an odd-leg jenny. If you have an adjustable combination square that you can set accurately to 45 degrees, then you don’t even have to measure anything – just run a 45 degree line in from each corner, and your hole goes at the intersection.
29 April 2011 at 19:32 #67701
Colin Jacobs 1
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@colinjacobs1
Been in the workshop and tried these, You can see the differance

Marked out using ruler and square.

http://www.flickr.com/photos/30854310@N02/5670464088/in/photostream

The drilled plate of this pic is on the left of the first pic

The tops are not quite square but I am filing it to get them better.

http://www.flickr.com/photos/30854310@N02/5670464586/in/photostream/#/

Now going to find out how to upload images you can see.

Edited By Colin Jacobs 1 on 29/04/2011 19:39:38
29 April 2011 at 19:42 #67703
Colin Jacobs 1
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@colinjacobs1
Pics can be seen in my album on this forum.
29 April 2011 at 20:18 #67705
mgj
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@mgj
Well perhaps im being a bit doddery in my old age, and the shaky hand provides a bit of a margin.

However, if I mark out from an edge using and engraved ruler to set my oddlegs, and an optical punch to punch the intersected holes, and drilling a clearance of.1mm, I reckon a set of holes should line up.

Of course if the job is properly complex then I use the DRO in hte mill in its SDM mode, but oddlegs are really pretty good for ruler type marking out.. Medium accuracy to scribe a line I use proper depth type digital thingy, but for marking out a line of rivets or the like, oddlegs are not too shabby.

Edited By mgj on 29/04/2011 20:18:52
29 April 2011 at 21:46 #67709
The Merry Miller
Participant
@themerrymiller
MGJ, I’m glad you mentioned the optical centre punch I’ve got to the stage now that I need one and I’ve just sent off for the “Dankroy” version (British made).
29 April 2011 at 22:12 #67711
Steve Garnett
Participant
@stevegarnett62550
Bit more analysis required here, I think. Judging from the pictures, the holes seem to be more inaccurate than the markings would suggest (although the spotting in the first one isn’t quite there, is it?)

So, how are you drilling the holes? It looks as though you’ve just gone for it with the size you want to end up with, and the drill has drifted. With a relatively small spot like that, I think that you probably need a relatively small pilot hole first, rather than one where the chisel edges of the drill almost certainly extend beyond the diameter of the spot. When you are in this situation, spots can sometimes make things worse than not having them at all, because just one chisel edge makes contact, forcing the drill to drift the moment any drilling force is applied.

So what I’d go for (even with relatively small holes like these) is initially a pilot drill which has a diameter slightly greater than the chisel edge of the drill you want to end up with, and then a final size drill. And also make sure that the work is securely mounted before drilling it – that makes a huge difference to the final positional accuracy.

Regards, Steve
29 April 2011 at 22:52 #67712
mgj
Participant
@mgj
Has he actually been told (Grannys etc!) how to drill a hole in the right place?

1. Mark hole with sharp scriber.

2. Centre punch – preferably with an optical punch IMO – but a punched hole in the right place you need, even if it has to be dragged by tapping with an ordinary CP.

3. Start with a proper centre drill. (Some will recomend a spotting drill?)

4 Then drill the hole – if its a big hole one will need a pilo – with a good sharp drill, and those are rarer than one might imagine.

Merry Miller – I love the optical punch. Most useful accessory (almost) I have. Mine sadly is not UK made – It has, for me, transformed marking out into a properly accurate procedure.

Edited By mgj on 29/04/2011 22:54:43
29 April 2011 at 23:25 #67715
Nicholas Farr
Participant
@nicholasfarr14254
Hi, I don’t have a optical punch, but what I do when I need to be fussy, is to use my autopunch on minimum and feel for the scribed lines and lightly put a small dot into position. I then look at it through a loupe, make any correction needed and then give it a decent dot for the drilling process.

Regards Nick.
30 April 2011 at 00:25 #67718
Steve Garnett
Participant
@stevegarnett62550
Posted by mgj on 29/04/2011 22:52:39:

Has he actually been told (Grannys etc!) how to drill a hole in the right place?

Judging from the pictures, I don’t think that Colin has quite grasped all of the implications of hole drilling procedures, no… and to be fair, there are several different ways of achieving an acceptable result, and we haven’t covered them all, or even found out what equipment he has at his disposal.

I don’t have an optical punch either, and I generally do what Nicholas does, too. But if I want really accurate positioning in the absence of an optical punch, I do the drilling on a mill with a DRO, and start with a centre drill.

The other thing worth mentioning in terms of getting a drill to start correctly is that this is also often a lot easier with four-facet or split-point drills, to the extent that for a lot of jobs you don’t need to centre or pilot drill at all if you use one of these.
30 April 2011 at 08:27 #67728
mgj
Participant
@mgj
Steve- I agree, an optical punch is not essential, and there are places where because of the design (of mine) you can’t use it, and you are back to the old way. I don’t have a loupe, but I do have a 4x panel in the bottom of my workshop glasses, which serves as well. But, where it can be used, an optical punch is a great help, I find.

(Like you, when I really mean business then the DRO comes into its own, and one doesn’t mark out at all, other than to use co-ordinates)

Four facet point drills are excellent, (just THE best IMO) but can you buy them? Or do you have to have a Quorn or similar?

Likewise split points – I do have some, but they were from a Dormer discontinued line. Did they discontinue all split points, or do they still do them?
30 April 2011 at 08:55 #67730
Les Jones 1
Participant
@lesjones1
Hi mgh,

Arc Euro Trade do split point HSS-Co drills. I only have a few of these (Tapping sizes.) but they work very well.

Les.
30 April 2011 at 10:48 #67736
The Merry Miller
Participant
@themerrymiller
Received the Dankroy optical punch in the post this morning.

What a cracking little device it is, beautifully made, even fitted with oilite bushes.
30 April 2011 at 12:09 #67742
Colin Jacobs 1
Participant
@colinjacobs1
Thanks for all the kind advice I am back in the workshop today taking on board all comments

I use an Axminster pillar drill and a 4mm jobber drill bit.
30 April 2011 at 12:15 #67744
KWIL
Participant
@kwil
Dormer drills with PS2 point is a good source of 4 facet, {Greenwood Tools) good at starting without a centre on a smooth surface.
30 April 2011 at 19:56 #67770
Colin Jacobs 1
Participant
@colinjacobs1
Yes just realised these jobbers soon go blunt, will invest in better drills this week.
30 April 2011 at 21:57 #67774
mgj
Participant
@mgj
Colin – its not the fact that they are jobbers drills- it just the quality. However if you get a lot of vibration as the drill engages (poor workholding?) then you’ll knock the edge off even the best.

I have to admit, nowadays I rarely use a jobbers length, in smaller sized holes. I always use the much shorter fast spiral stub drills – much more stable. Occasionally a stub drill isn’t long enough, but not often
30 April 2011 at 22:13 #67775
Colin Jacobs 1
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@colinjacobs1
That’s what I got (chatter) so I must clamp the vice so it does not move too, will carry on practicng this weekend

Thanks.
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