Advice on Cluttered Dimensions in Drawings

Ian

I will take notice of you when you publish your personnal profile.

JA

So taking circlips 8 holes, say a 4 * 2 array. With daisy chained dimensions the diagonal could be out by somewhere around 4 times the general tolerance. Of course if your marking out is perfect it doesn't matter, mine isn't. There might be places where one datum isn't appropriate, but this would be the exception. Ordinate dimensions make the drawing less cluttered.

And I'll echo the plea, can someone find a copy of bs308, send it to whoever does the drawings for ME and MEW

Edited By duncan webster on 21/03/2022 14:57:12

My dimension question came up during an excursion into 3D printing, and I've been distracted by a USB cabling problem, still unsolved.

Many thanks for the help and observations, all much appreciated. It's been underlined to me that producing good drawings is a mixture of art and science. Science does an excellent job of the geometry and correct drawings, but making clear to a human needs intelligence!

The Coupler is modelled in 3D with a Pad and 3 pockets, 4 simple sketches total. The sketches make perfect sense to the CAD package, but not in a workshop. Though the rendered object gives a good idea of the shape and how it might be machined, it's not dimensioned.

3D printing is easy enough because the CAD model contains all the information needed to create the shape. Ditto CNC. For strength I need to make the coupler in Aluminium or Mild-steel, and I only have manual machines. Proper 2D Technical Drawings are needed.

Here's the range of 2D plans and projections FreeCAD (and most other modellers can generate):

Unwise to print all of them with internal detail, centre-lines, dimensions, tolerances, labels, sections and balloons etc. In this case, I think the coupler can be completely described by the Front, Top, and Right Views, and it's helpful to add the Front Top Left and Front Top Right isomeric projections. A simple text description bottom right is needed: Title, Date, Name, dims in mm, material=Aluminium, Third Angle etc

I'm taken by JA's "More Paper" suggestion. I can only print A4 at home, so one page for the general arrangement plus a page each for the individual views, as necessary to remove clutter.

Otherwise, I'm going to experiment with the other suggestions, like Jason getting rid of angled arrows by using linear dimensions instead. Watch this space!

On the great chain vs don't chain debate, my First Year draughtsmanship books all advise against it because it can cause errors to accumulate. As there are examples of short chains in the same books, I guess it's not always wrong! When milling, I prefer to work from a small number of reference points, which is easier when dimensions aren't chained. Again, the idea is to avoid small errors adding up into a big problem at the end.

Back to my 3D printing problem now, then another go at dimensioning.

Many thanks,

Dave

Time to settle down with beer, nibbles and a dictionary, pausing only to don appropriate PPE against flying toys.

Andrew

If a drawing starts to get too cluttered with dimensions I do all X axis dimensions one layer and all Y axis dimensions on another, then I can print off two drawings for the workshop that are easier to read.

Dave as it's now clear it's for home use then no real need to worry about the latest BS standard or dimensioning styles just do it to suit the way you are going to machine it. It's only if you are going to make the drawing available to others you need to give it a bit more thought.

Although I do a 3D model of all my engines and check holes line up and moving parts like cranks and conrods won't hit anything when turning I seldom print off drawings for use in the workshop to actually make the thing from. Typical 3D of the one I'm currently working on. I just take off what sizes I need from the 3D part and get on with making it

I hope this won't make anyone choke on their but this is what it's built from, I think there is even an envelope or two in there and just one printed drawing.

But it seems to work for me as yesterdays little video shows. If it's going in the mag or for work then I'll approach things a bit differently

Edited By JasonB on 21/03/2022 16:22:26

That's a good idea and I can steal it for my go to 2D drawing package, QCAD.

Unfortunately doesn't work for FreeCAD-Techdraw because it has no layers! (One reason why FreeCAD warn against using Techdraw for stand-alone 2D drawing: as it's meant for generating 2D drawings from 3D models it lacks many ordinary drawing features.)

Dave

Jason's approach is mostly how I do things now. Creating the 3D model does most of the thinking required to make the part, and I find that a few dimensioned sketches are usually enough to actually do the job.

Which means a drawing from the model only really needs to be clear to you. The examples above should be enough to allow you to do that.

I wish programs like Fusion or Alibre allowed you to add visible dimensions to the live 3D views, as that would be even easier - no drawings with all the fudges required to represent 3D objects as elevations no longer needed at all.

.

It’s personal preference, of course, but: Based on my preferred way of machining [with either a rotary table on the BCA, or with a drilling head on the lathe] I would much prefer see the centre of the cylinder as a datum and the mounting hole centres dimensioned by polar co-ordinates.

Each to his own

MichaelG.

Me too: perhaps the biggest advantage of 3D modelling is the way it power-assists the thinking process. I also end up working from a pile of paper notes and sub-standard drawings derived from the 3D model. Jason's photo could have been taken in my workshop:

But the approach is only suitable for singleton workers. I think it's still necessary to produce good 2D technical drawings whenever a design has to be built by others manually. The 3D-CAD to notes technique works well for me, but I doubt the readers of Model Engineer Magazine would be happy with that approach.

There are worse sins than clutter. Missing and incorrect dimensions and datums; dimensions that look right on individual drawings, but parts made from them won't fit together; mixed units; too thin lines; weird abbreviations and symbols; irrelevant or too few dimensions; and fractions!

Dave

Ordinate dimensions can help with 'de-cluttering', and work well with a DRO-equipped mill.

Take care though, that you don't do what I did last weekend and read the last hole position as the length dimension of your workpiece. Its exceedingly annoying to find that the last of the numerous holes that you've so carefully, so precisely, drilled lies on that misplaced edge...

It will either be on the forum or possibly in the mag. If in the mag I better tidy up that pile of drawings but that is the sort of thing that sometimes gets sent in so I think the designer does quite well producing the drawings from that sort of material.

And hopefully, the graphic artist that tarts them up for the Mag. will get all the dimensions correct.

Regards Ian.

Looking forward to seeing the engine in print - it's another cracker.

I've not noticed any quality issues in Jason Ballamy publications, so how is the 'tidy up' done? Do you work from the 2D drawings produced by the 3D-CAD tool, redraw them from the working Notes, or what?

My interest in technical drawing is partly because I enjoy doing them well, and partly because I want anything I share with others to be clear. I often fail, so very much a work in progress!

I feel for the magazine editors if they have to make proper drawings from the sort of rough jottings I use in the workshop! No wonder mistakes creep in.

I've fixed my USB/3D-Printer problem, so might be able to play with dimensions. Except I ought to load the car with junk and visit the tip...

Dave

Dave, it's a number of things.

As I build I may make small changes and try to update the 3D model as I do, so checking that is up to date is one thing.

I may well have drawn parts that I have machined on the CNC but as most don't have one I may tweak a few features to make it easier for those with manual machines. or draw up alternatives.

Then I'll start drawing, if going into the mag then A4 suits as Martin can shrink it down to A5 and get two drawings to a page so designer does not get involved. So I have to bear this in mind and mot make parts too small that they are hard to see at the reduced size though not a problem for digital subscribers. Those actually making one of my designs in ME usually end up with the A4 drawings anyway.

I'm also aware that putting one sheet on a page will not make subscribers happy as it will bulk out the length of the article so will try and group smaller related parts together on one sheet but try not to overcrowd it.

People also seem to like a BOM so I'll pull one of those off the assembly and use that as a basis for a table.

Not sure where this one will end up as on the one hand it could see sales of Stuart cylinders and flywheels increase but on the other it may see sales of the Real kit decrease so it may be better kept to the forum(s) where I can freely post my thoughts on castings for casting sake etc.

Thanks Jason, good hints. I like a BOM.

This is the fruit of this afternoon's interrupted labours, no peace for the wicked:

Happier with this, done by spreading the dimensions across views. Need to try a more complex example though - the coupler is pretty simple. Delighted to get more suggestions.

Dave

Rather than writing 'third angle', where you have to remember what it means, the industry norm is to have the elevation and end view of a bucket, normally place centre bottom of sheet where I worked

We rely on the goodwill of hard working people who effectively volunteer their time to create drawings for our hobby (I know the magazines pay, but lets face it most are doing it for the benefit of their hobby rather than to line their pockets). The drawings are not going to be perfect all of the time, but there are people still producing them despite a wave of hostility from onlookers. We should be grateful rather than trying to tear them to pieces. This is a hobby largely full of enthusiastic amateurs.

One of my most vocal critics at the model engineering society I attend has frequent, loud advice for me, usually prefaced with "you know what you are doing wrong..." or "you know your problem don't you...". This is from someone who once let slip he last used a lathe at school, 45 years ago, and has driven a locomotive once. But the advice keeps coming.

Nice, polite advice is always welcomed, especially from those who maybe had careers in whatever the subject at hand is. But sometimes the holier than thou snobbery on this forum is nothing short of discouraging. Calling out others opinions as rubbish, belittling others, all this crap, it really needs to stop. It's just elitist attitudes that will kill our hobby dead.

Well said Jon

Rob