Engineering measuring, templates....??

[GrahamRounce]

Hello. I'm not sure this is the right forum, but it's the nearest I could guess.

I'm currently making measurements, cutting, marking points for holes etc etc etc, in wood, metal and plastic using the most basic devices, eg a ruler and calipers. But everything ends up fractionally off, no matter how careful I try to be.

I'm guessing that for real engineering work there must be any number of jigs, templates, guides, gadgets, whatever, for enabling spot-on accuracy. Of course, I don't know what any of them are.

Can anyone suggest a book or other source from which I can at least learn what's available?
Thanks,

 

[GrahamRounce]

For instance, one good thing I got at a market, rather superceded by the digital calipers, is this collection of measuring blocks. They must be quite high accuracy, as they can be "wrung" together.
Anyway, I'm still thinking more in terms of accurate hole placement, finding the centre of an eg plank, etc etc.

 

[Rich C]

How much off are you? I've not found any issues with using a ruler in general, though I do find a laser measure handy for longer distances.

Are you marking with a knife or similar thin edge?

 

[CHJ]

1. Are you measuring 'one off's '
2. Measuring repeat items individually.
3. Measuring mating items individually.

4. Or using a storyboard to transfer a 'one off' measuring exercise to repeat items.

 

[Phil Pascoe]

https://www.pettigrews.org.uk/lm/page030a.htm

one pencil only for finding the centres of boards.

 

[MusicMan]

The 'proper' way, short of a coordinate measuring machine, is a small surface plate (30 cm is enough for small bits and pieces) and a vernier height gauge (again 30 cm is enough for small bits). The vernier height gauge should have a hard (carbide) scriber on it. Cover thinly the metal being scribed with engineers' blue, lay the piece on on edge, then you can scribe an accurate line parallel to this edge. Do this on an adjacent edge and you get two crossing lines. With a dot punch in reasonable condition, you can feel the groove and intersection of these lines, and place a punch mark for drilling to a precision of about 0.1 mm. Of course this is for metalwork, you don't need it so precise for woodwork; in that case a sharp pencil or a marking knife is normal.

I recommend the Workshop Practice series of books to find out more. The Basic Benchwork volume is a good place to start.

https://www.amazon.co.uk/Basic-Benchwor ... 28&sr=8-16

 

[GrahamRounce]

Ok, thank-you.
I should have given examples of the difficulties...

For instance:
Drilling a series of holes in a line, equally spaced.
Finding and marking the centre of a small area (eg 2cm x 1cm)

I understand that a long pivoted guide bar will give a much better accuracy near its pivot as the far end is adjusted.

(I made a wardrobe using only a "measuring stick" and a marking knife, adding various thicknesses of the tiimber as necessary, and that worked very well, much better than measuring things with a ruler & pencil. Just fyi.)

 

[CHJ]

...
For instance:
Drilling a series of holes in a line, equally spaced.
…..

If you need to do this say on a cupboard side to provide shelf support peg holes then a simple jig with a peg and drill guide hole can be advanced along the row as you drill the holes. You can use a spare drill shank as your 'peg'

a lip on the long edge will give you consistent edge spacing.

If you have a lot to do then use this method to produce a longer jig with multiple holes that can be clamped in place whilst you drill the complete row.

If you want to drill in the middle of a space then try measuring equal distances from the sides 'boxing in' the central area.
Spotting this area with the tip of the drill gives you a good reference as to whether you are aligned correctly before proceeding.

 

[Rich C]

Also brad point drills are easier to start accurately.

 

[GrahamRounce]

Ok, thank-you.
No "special things" used by real engineers, then?

Proper factory stuff is always spot on, as are model steam engines etc, indistinguishable from factory stuff..

I thought someone was going to say. "What you want is a rectangle centre-finder-marker". Or a plank centre-finder. Etc etc.

You can get things with lots of circles of holes for something or other on a lathe, I think... that kind of thing... for real accuracy.

I know it's possible to wangle your way around it. So is making a right-angle, but who wouldn't use an engineering square to get it dead right?

No?
Thanks

 

[CHJ]

MusicMan started you on the corrected path for 'proper' engineering practice and accuracy.

The 'proper' way, short of a coordinate measuring machine, is a small surface plate (30 cm is enough for small bits and pieces) and a vernier height gauge (again 30 cm is enough for small bits). ….

Add a few more precision tools such as slip gauges, a sine bar, calibrated Vee blocks Dial gauges and away you go.
All the former are the tools of the precision Model Makers you refer to, there are no quick easy options for engineering precision.

And where you can't use the basic tools to mark out the workpiece or set up the machine for the above you use them to make a specialist tool[Jig] that will give you the ability to transfer the precision required onto the work.

 

[TheTiddles]

This is a curious question, or at least the way of asking it.

There are many ways of getting woodwork right, but in general you need precision far more than accuracy, I.e you want several pieces of wood the same length, the fact that they are all slightly longer or shorter than desired is often of lesser importance. Do this with fixed fences, jigs etc... Used in a careful order so you don't need to change the setup, therefore precision is maintained.

As for engineering, it's kind of a big subject but as a general rule, to get two holes an exact distance apart... You don't, it's impossible, one hole and a slot, compensate in your design such that the precision isn't needed, that's engineering.

Oh, and making model steam engines is not engineering, it's metal work.

 

[Trevanion]

If your holes are off but your marking is spot on, are you using proper drill bits for the material and the correct preparation techniques? As drill bits tend to have a likening to wander off-mark if you're either using the wrong bits or preparing the material incorrectly or not at all.

Woods: Brad-point drill bits ideally with hole locations marked with an awl before drilling but not totally necessary. It's very hard to get dead-accurate holes in wood, trying to be engineer accurate in a material that moves after being cut is just fools-play.

Metals: Centrepunch every hole location so that the jobber drill has a place to rest in when drilling thus resulting in the drill bit not wandering, it's also good practice to pre-drill with a smaller drill bit for sizes larger than say 6mm. Bit choice depends on the material, a regular jobber will go through most materials but will snag in brass so it's worth having a second set with the cutting edges "brassed off" which involves effectively dulling the front of the cutting edge to a neutral rake so that it doesn't bite. Hardened steels will require harder bits than standard HSS, for example, Cobalt Steel, Carbide and Diamond drill bits will drill hardened materials. With holes that I want to get spot-on on the pillar drill, I will start the cut with a centre drill which is just a very short stout drillbit designed for drilling centres in the lathe, the stoutness and stubbiness of the drill helps to eliminate any drill bit wander and give an exact hole for the real drill to follow.

Plastics: Not one I work with often but there's a massive variance in techniques depending on what plastic is used. I find brad-point bits with a shortened point work excellently in most plastics but jobbers work better in Nylon and Delrin from experience. There's even special drill bits to be had that are specific to certain plastics.

Sorry if this is very basic information you already knew and I'm trying to teach a granny to suck eggs but it's quite often overlooked.

 

[AndyT]

In metalworking, there is a technique for getting a line of holes very accurately spaced, using toolmaker's buttons - this may be the sort of thing you are asking about.

I've no experience of using them but there's plenty of info online or in the books mentioned. This is one site explaining them https://johnfsworkshop.org/home/tools-f ... s-buttons/

As the writer notes at the end, in modern practice the machine used would have an accurate DRO (digital readout) of the cutting tool's position, often making measurement on the workpiece unnecessary.