Any tips for working at higher precision? e.g. Do you do this?

[Donald MacDonald 1Participant @donaldmacdonald1]

[Donald MacDonald 1Participant @donaldmacdonald1]

Hello

I thought I would share this technique. I am wondering if it is a standard way of working.

Simply put, if my pen is really too fat for the job in hand, I draw a long thin L shape and work from the 'far' edge of the L.

e.g. In this photo I am trying to measure exactly 10mm. To mark it I have drawn a rather fat blue line with my 0.5mm Frixion pen (which has the advantage of be erasable cleanly, without any rubbings). The red dotted line is the line I will need to cut the (white) material which I am marking.

NOTE: "For good measure", in this case I have used a steel block to butt up against the white material, so that I can use my engineering rules (i.e. rulers which have no lead-in and start at zero), to make 100% sure that my measurement is starting precisely at the edge of the white material.

Discussion
It seems to me that the only down-side of drawing from the edge of an "L", (rather than from the centre of a short line – that is hopefully drawn with a thinner line), is that it's a bit more time consuming to remember which side of any given marking one is supposed to be working from!

Also when marking out more complex shapes it quickly becomes confused if one is working on the EDGE of a line rather than the CENTRE of a line.

Which is why I started this thread:
"Need a pen to draw the 'finest possible' lines?"
https://www.model-engineer.co.uk/forums/postings.asp?th=179283

So when you folks are needing to work with great precision:

– Do you folks tend to draw Ls or short lines?
– What other tips & techniques can you share that help with your accuracy?

Cheers

Don

 

Edited By Donald MacDonald 1 on 19/04/2022 13:36:23

[pgk pgkParticipant @pgkpgk17461]

Depends what you're doing with the line afterwards and precision is a relative thing. On a piece of metal my best method would be using a marking gauge on a surface plate with the sheet against a square block. Or simply using preset caliper jaws with one along the metal edge. Since you have erasable ink (or marking blue in my case) one would mark through it. Another alternative would be a10mm wide item lined with the edge and mark along that. Yet another option available to me is to pop a scribe or pencil etc into the mill and use the DRO to measure.

pgk

[Speedy Builder5Participant @speedybuilder5]

I was taught to never measure from a drawing as the paper, film etc could not be guaranteed stable. However, that being said, measurements were taken from 'lofted' lines drawn onto aluminium alloy sheets and mylar film !

Bob

[SillyOldDufferModerator @sillyoldduffer]

Is this marking out paper to cut it accurately, or drawing accurately?

If the latter, I try to avoid, and professional drawings often carry the instruction DO NOT SCALE, which is a strong hint to use the dimensions given, not the lines. Making from the drawing involves all sorts of tricks depending on what's available and the precision required. For example, when milling, I clamp the object firmly to the table, and make or find a fixed reference point from which the DRO is set, and can be reset. Then the DRO scale is used – mine displays to 0.01mm, but is only trustworthy to about 0.02mm: if better than that, I switch to ground blocks, calipers, micrometers etc which is 'good enough' for what I do, and not too much bother. For better than that I've got a book on Toolroom methods, of which the only one I've tried is Buttons – they position holes more accurately than a drill.

I don't see paper as a precision material by metalwork standards. Metalwork is routinely done to within 0.02mm/0.001" . That's significantly more accurate than woodwork because wood is too unstable for precise work – it stretches and reacts to humidity. So does paper.

Marking out woodwork style trying to get a littlebetter than ¹⁄₁₆" I cut on the edge. Critical lines are drawn between two dots and the cutting side marked with a chevron because I have a terrible memory.

Wherever possible I use mechanical methods to improve cutting: I'm a clumsy oaf and hand tools don't work well for me! Clamped guides, templates, guillotines etc: anything I can think of to keep cutting tools straight.

Dave

[Donald MacDonald 1Participant @donaldmacdonald1]

> Is this marking out paper to cut it accurately, or drawing accurately?

I was talking about marking materials including card, paper & plastic for cutting. And also when cutting metal  material roughly.

When cutting out metal more precisely I would try to use Dykem Steel Blue layout fluid, and then mark it with a scriber… but it isn't always possible/practicable particularly for larger objects.

Personally my drawings I always do digitally (2D illustration package or 3D CAD), although I may wish to annotate/correct the printouts by hand, before the design is added back to the 2D/3D CAD. Although of course before any of that happens I will often do sketching by hand, before turning it digital, but – by definition – no accuracy would be required for that.

But my above technique of marking with Ls with one long leg/line and one short leg/line has greatly helped me avoid errors, although on has to make sure that one leg/line is significantly longer than the other. The down-side is that it's slightly more time consuming, than making a single short blob and then (presumably) aiming to cut down the centre of the line.

Edited By Donald MacDonald 1 on 20/04/2022 20:32:57

[Bill PudneyParticipant @billpudney37759]

When I was doing my apprenticeship in the mid 60s, we had to do lots of training courses to attempt to get a bit better. Obviously these are all outdated by now but they can be some relevance.

After some training we had to get a decent wood back pencil (Faber Castell, or Staedler (??) or similar) and then sharpen it with a chisel point, and then draw a series of that point and see how measurement you could measure. Obviously all rules were steel rules and some had the big advantage with metric. Anyway has far as I can remember we were fairly good and drawing over 0.1 mm (ish) were not to difficult. Then there was the test at drawing parallel lines, at 1/64" apart. Then we had to write the alphabet between the letters. That was a challenge, but it was achievable.

The best pencil was a 6h which was pretty hard. When I moved into the DO, my trainer insisted on using 8h pencils, and part of the checking process was to ensure that the line could be felt on the reverse of the tracing paper.

Obviously this would now be a bit difficult these days………..

cheers

Bill

[HOWARDTParticipant @howardt]

In my training days taught to use a chisel point, H and 2H on paper then later used a flat lead Fedra Constructor refillable pencil. Only ever used to measure an original drawing, prints can vary in all directions, even plastic film is not temperature stable. Now a days all the drawings we handle are prints in one form or another. When lofting all done on heavy weight film everything was created with compass and straight edge as these were used for actual build comparison during checking finished parts, usual aircraft related.

[not done it yetParticipant @notdoneityet]

I was talking about marking materials including card, paper & plastic for cutting. And also when cutting metal material roughly.

Cutting material roughly doesn’t incur too much precision?

[Martin ConnellyParticipant @martinconnelly55370]

I hope all this hard work is being done in a temperature and humidity controlled environment. I have to ask what is the purpose of all this precision? Most of us work to different levels of precision in order to meet the needs of what we are doing. Theoretically I can draw a very thin line using CAD and print it off accurately positioned relative to other thin lines but then what? Cut it with scissors that tear the edge, cut it with a knife that pushes the edges away or just say "Look what I can do"?

Martin C

[Martin Johnson 1Participant @martinjohnson1]

My short answer for metalwork is to not do it that way. Surface plate, rule stand and scribing block or vernier height gauge are the right tools for precision marking out.

Martin

[Robert ButlerParticipant @robertbutler92161]

In answer to the original posting No and No

Robert Butler

[Author]

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