Precision layout & machining?

[Dianne BestParticipant @diannebest69516]

How to book?

[Dianne BestParticipant @diannebest69516]

I have been machining off and on most of my life but mostly for big stuff and old machines where 0.001" is good enough.

I am now wanting to make some smaller models and need to improve my layout and machining techniques to improve the accuracy by an order of magnitude.

Is/are there any good books (preferably eBook) on precision machining? What do you recommend?

Thanks gang!

[NJHParticipant @njh]

Good grief Dianne I would hazard a guess that 0.001" is good enough for most folk here ( with the occasional "guesstimate" of half a thou! maybe).

I look forward to seeing some of your creations.

Cheers

Norman

[JasonBModerator @jasonb]

I do far less layout than I used to since I got a DRO on the mill, now I will just find the edge of the work and use the DRO to position holes and surfaces.

J

[WatfordParticipant @watford]

Dianne,

If you are really going for gold then may I suggest "Accurate Tool Work" by C.L. Goodrich & F.A. Stanley.

Original copyright by Hill publishing Company 1908, and reprinted 1988 by Lindsay Publications Inc

Old it may be, but for layout it does tell the whole story. An interesting read for anyone interested in engineering.

Enjoy

Mike

[Rik ShawParticipant @rikshaw]

Hello Dianne – Like Jason I use the DRO on my mill for “jig boring” instead of marking out whenever it is possible.

Sometimes however, I like to do things the old way and mark a job out instead. For marking out I use a digi vernier height gauge fitted with a carbide scriber wedge along with a set of slips. To complement this and because my eyes are not so good when it comes to aiming the centre punch accurately, I have a Dankroy optical centre punch which gets the pops dead on position. I paint a copper sulphate solution on jobs as a marking out fluid but DYKEM blue would be the better choice I’d suggest.

Plenty of freely available info online re: advice and tips – have you tried this one?

**LINK**

Rik

[colin hawesParticipant @colinhawes85982]

There is no point in trying to machine most work to better than 1 thou unless it is for a special fit. My old 1927 Drummond can do that comfortably but if you are trying to obtain super scale accuracy you should consider that the drawings' dimensions have been rounded to a greater error than 1thou, threads have to be standard and higher accuracy probably calls for grinding for consistent results. Good finish and accuracy relies on sharp tools and constantly checking size and polishing with emery can give the finish most people want. Colin

[HOWARDTParticipant @howardt]

As others have said or alluded to, model engineering is about making some thing work not precision per se. When we worked as engineers precision depended on the trade and size of things. A micron for some was as near as ten millimetres for others. Mostly we are dealing in one offs as well. if the hole is a little undersize we can make the shaft a suitable fit ignoring the size. Also unless you are dealing with drawings from an engineering draughtsman I suspect it will have no tolerances on any way. You can of course go the precision machining route, but that would entail precision machines and measuring equipment to match. I for one cannot afford the precision route, i did buy a new slip gauge set for £100 noting that it wasn't in the same league as a precision set at £2000, but it is good enough for what I do.

[Tim StevensParticipant @timstevens64731]

If anyone was able to make a locomotive at exact scale (say 1:10) then I am sure it would not work. The bearings would be too tight, and the pipes too small, for example.

An order of magnitude down from 1 thou takes us into fine grinding, to get +/- 0.0001. And who will notice?

Cheers, Tim

[Dianne BestParticipant @diannebest69516]

Okay, so maybe 0.0001" is a bit of an exagerataion but definitely to 0.001 +/- half a thou.

I have always envied those who can layout a bolt circle of 6 or 8 #4 screws on a 2" diameter with such precision that the cover fit in any position – I can't do that! I want to be able to.

[JasonBModerator @jasonb]

As Rik says if you want to layout things accurately then leave the rule in the toolbox. A height gauge works very well and can be set to 0.001" or a bit less quite easily. Once you have your pair of lines ( use co-ordinates not a scribed circle) you will then want to think about using an optical ctr punch and checking the dot with a magnifying glass before punching deeper. This is how I do it when not using the DRO

How do you do your drilling at the moment, with a drill press or do you have a mill? If with a mill then even without a DRO you can get good accuracy using teh handwheels and co-ordinates provided you allow for any backlash.

Alternatively use a generous clearance hole

Edited By JasonB on 22/10/2016 19:18:34

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dianne Best on 22/10/2016 19:05:28:

I have always envied those who can layout a bolt circle of 6 or 8 #4 screws on a 2" diameter with such precision that the cover fit in any position – I can't do that! I want to be able to.

.

… A decent Rotary Table will do that easily

If the thing is defined in Polar co-ordinates, then use Polar

Translating to Rectangular co-ordinates introduces a layer of abstraction, which will inevitably produce approximation errors. [Yes, I know they can be small, but …]

MichaelG.

[Ian PParticipant @ianp]

Posted by Michael Gilligan on 22/10/2016 20:36:39:

… A decent Rotary Table will do that easily

If the thing is defined in Polar co-ordinates, then use Polar

Translating to Rectangular co-ordinates introduces a layer of abstraction, which will inevitably produce approximation errors. [Yes, I know they can be small, but …]

MichaelG.

I'm not convinced about the approximation errors.

Errors due to translating between coordinates can easily be completely insignificant, it could be done to umpteen decimal places.

My main point is though that a rotary table might put all the holes on a true circle and all might be the correct angular distance apart but the diameter of the circle still has to be correct.

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ian Phillips on 22/10/2016 21:09:09:

I'm not convinced about the approximation errors.

.

That's fine, Ian … I was only expressing an opinion.

For a simple practical example; look at the spec sheets for the fixing holes on NEMA stepper motors: Many of these quote rectangular co-ordinates; but the things were designed with four equispaced holes on a pitch-circle.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

< sorry; double post >

Edited By Michael Gilligan on 22/10/2016 21:37:35

[AjohnwParticipant @ajohnw51620]

Accurate tool work is on the internet archive but as sometimes happens when some one has nicked it and printed it there are missing images. What's in it though should give you some idea if it's worth buying.

If you want to fit a dro to something this site might interest you

**LINK**

For self fit self made scales Renishaw might be of interest.

Most DRO's will work out co ordinates for various things.

It can also sometime be possible to drill holes on mating parts in one go or use some sort of drill jig for both parts preferably hardened if it is going to see a lot of use.

I agree with MG on the rotary table aspect – providing there is some clearance on the screws. The clearance sets the precision that is needed. 0.001" scales on many machines can be read to at least a 1/4 of that and as the same scale are used for both parts the dimensional accuracy of the thou's doesn't generally matter. Wear may have some effect of course. If a DRO is used then the repeatability and linear accuracy of that sets the accuracy that will be achieved.

John

–

Edited By Ajohnw on 22/10/2016 23:49:59

[JasonBModerator @jasonb]

Before I had the DRO I did not use the rotary table to drill holes on PCD, always whipped out the Zeuz book and used co-cordinates. If both parts are done with the same method then there should not be a problem. I also find it easier to mount a large casting straight onto the mill table rather than try and get it concentric onto a rotary table and loose head room at the same time.

Something like this would be hard to get true on a rotary table or under a BCA's spindle

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 23/10/2016 07:36:12:

Before I had the DRO I did not use the rotary table to drill holes on PCD, always whipped out the Zeuz book and used co-cordinates. If both parts are done with the same method then there should not be a problem. I also find it easier to mount a large casting straight onto the mill table rather than try and get it concentric onto a rotary table and loose head room

Something like this would be hard to get true on a rotary table or under a BCA's spindle

.

All very reasonable, Jason

… but Dianne is specifically seeking improved precision, rather than convenience.

[quote]

I have always envied those who can layout a bolt circle of 6 or 8 #4 screws on a 2" diameter with such precision that the cover fit in any position – I can't do that! I want to be able to.

[/quote]

MichaelG.

Edited By Michael Gilligan on 23/10/2016 08:39:43

[john carruthersParticipant @johncarruthers46255]

On a practical note, I found a magnifying centre punch and a set of magnifying goggles a huge boon, improved my drilling accuracy no end.
I have 2 sets of marking out and measuring tools, one rough set that stay on the bench, and the 'best' set that live in their boxes and only come out on high days and holidays.

[Dianne BestParticipant @diannebest69516]

Posted by john carruthers on 23/10/2016 08:53:11:

On a practical note, I found a magnifying centre punch and a set of magnifying goggles a huge boon, improved my drilling accuracy no end.
I have 2 sets of marking out and measuring tools, one rough set that stay on the bench, and the 'best' set that live in their boxes and only come out on high days and holidays.

That makes a lot of sense John. I never heard of an optical centre punch before but it is definitely on my list now!
A second set of measuring and layout tools also makes sense.

I am thinking about some type of magnification and better lighting as well for the layout area. The old eyes aren't as sharp as they used to be

[Tim StevensParticipant @timstevens64731]

Axminster do two versions of an optical centre punch – their own and one from Veritas.

They advertise on the right of this page …

Cheers, Tim

Edited: Well they used to, I'm sure.

Edited By Tim Stevens on 23/10/2016 11:24:58

[EmgeeParticipant @emgee]

Posted by Michael Gilligan on 23/10/2016 08:35:52:

All very reasonable, Jason

… but Dianne is specifically seeking improved precision, rather than convenience.

MichaelG.

I believe what Jason describes satisfies what Dianne wants to achieve and it is a convenient way to do the job but accept there are other equally accurate methods.

It does show that you don't have to use a scriber and rule or even a height gauge with scriber, optical centre punch and further magnifying aids to mark and ensure the drill is on centres for the 6 or 8 holes.

Emgee

[AjohnwParticipant @ajohnw51620]

I use a decent clamp on desk magnifier with a light and also have some Russian binocular loupes for if I need to be really manic. When buying those it's best to make sure that they are adjustable and have a sensible working distance. They were a right pain to set up. Can't see them on ebay any more but there are plenty of others

**LINK**

More often I have some glasses that the optician did for me for close work. It's not a good idea to use glasses like those a lot. It will just weaken the eyes more. Most of the time I just use well made 1.5 dioptre reading glasses from the chemists.

If you go for a surface plate and angle plate etc plus a height gauge I would buy a vernier one. The digital ones have this nice habit of the battery being flat when needed. The Mitutoyo ones often crop up at very reasonable prices.

The other thing I have is fold out hand magnifier. The fact that it folds out prevents it getting dirty. The one I use most is 2" dia so hard to loose. I also have a fold out jewellers type for higher mag if needed. And a measuring loupe from RS. I should point out I have varied interests and some of these come into that.

To be honest the only time I am likely to use the optician's glasses is when looking at buying a used machine. The binocular loupes hardly ever come out. The 1 1/2 dioptre glasses make my vision reasonable  but not brilliant from 18" or so. That's how I selected them. The opticians one, pin sharp up  to a few feet.

John

–

Edited By Ajohnw on 23/10/2016 11:51:50

[JasonBModerator @jasonb]

If you are going to Lee Valley to get theTaig they will also have Veritas products, I use their optical punch. There have also been a few designs in the model engineering press if you wanted to make your own.

[Rik ShawParticipant @rikshaw]

Dianne – As I posted on here a short while back I have bought one of these for close work. Comfortable on the head it flips up and down as needed over the top of your reading glasses if you use them. I have only used it for a couple of marking out jobs in the short time I have had it but it is a real eye opener. Thoroughly recommended if your eyes need a “treat”. (I chose the x 2.5 mag. lens which suits me perfectly.)

About £50 on ebay.

**LINK**

Rik

[Author]

Posts