Author Topic: Diamond Drag Engraver  (Read 13291 times)

Offline awemawson

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Diamond Drag Engraver
« on: December 13, 2013, 03:41:23 AM »
This is my take on a spring loaded 'drag engraver' for my CNC mill. Nothing particularly unique, just my take.

I wanted a co-axial design that would fit in a collet, so that it could just be one of the tools to select from the 16 way tool magazine. I made an air turbine driven engraving spindle years ago, and that can only be mounted manually as the airline needs connecting so cannot easily be part of a tool selection sequence.

Searching around, the diamond tips sold for Dremel engravers seemed the cheapest for experimenting. they are about 1/8" and 1" long. I had some phosphor bronze 3/8" bushes left over from a project many years ago, so they were pressed into service. The housing is a piece of 5/8" re-bar turned down to 15.5 mm and bored 1/2" for the bushes. For what it is, the re-bar machined remarkably nicely.
Andrew Mawson
East Sussex

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #1 on: December 13, 2013, 03:44:53 AM »
So how well does it work? Not bad at all for a quick cheap and cheerful projectette  :ddb:

The armature that holds the diamond point is currently mild steel, and measuring 0.373" is a '2 thou lose' in the bronze bushes. I've got some precision ground silver steel on order to replace it however with a non rotating spindle you would hardly notice it.
Andrew Mawson
East Sussex

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #2 on: December 13, 2013, 03:52:13 AM »
I'm using FeatureCAM to generate the tool path, and had to iron out a few quirks. For the engraver not to rotate, in the tool definition I was putting RPM = 0. It turns out if you do this, FeatureCAM automatically overrides the feed rate to zero  :bang:
Also the TNC355 controller on the mill strongly objects to spindle speeds below 50 RPM. Now FeatureCAM always issues an 'M03' (Spindle start) after it has called for a tool change. What I've had to do is re-code a bit of the FeatureCAM post-processor, so that if the RPM is less than 50 it outputs 'M05' (spindle stop) instead of the 'M03', then define the tool RPM as 30.

Now both the controller and the CAM package are happy - it's just like quarrelling children  :lol:

Andrew
Andrew Mawson
East Sussex

Offline RussellT

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Re: Diamond Drag Engraver
« Reply #3 on: December 13, 2013, 05:37:54 AM »
Hi Andrew

That looks really useful. :clap:

How big are the letters you've shown?

Russell
Common sense is unfortunately not as common as its name suggests.

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #4 on: December 13, 2013, 05:45:53 AM »
Those are about 8mm high.

Andrew
Andrew Mawson
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Offline Pete W.

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Re: Diamond Drag Engraver
« Reply #5 on: December 13, 2013, 06:49:18 AM »
Hi there, Andrew,

Yes, that looks interesting.

I do have some questions, though.  If you're going to engrave alphanumeric text, do you have to programme each session individually?  Or do you programme a font set of letters, numerals & punctuation characters and then call them up in something like ASCII?  With a parameter for font size?
If you're engraving with a diamond point, I guess you'd have to define character size in carats!   :lol:   :lol:   :lol: 

Years ago, I tried to interface a Hewlett Packard digital plotter to my Mac SE using some software called MacPlot.  As you may remember, fonts were quite a thing with that generation of Macs.  The only problem was that there wasn't a cursive font so MacPlot printed alpha-numerics by emulating a dot matrix printer, with the danger of wearing out the plotter's pen lift solenoid!   :bang:   :bang:   :bang: 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #6 on: December 13, 2013, 07:16:46 AM »
Pete,

You can use any font that Windows has available to it, or if you are really desperate define one yourself. The modern software makes things really easy compared to 'how it was'. You can define font size, various enhancements such as bold or italic, give it a curve to align the text to, reverse it as in mirror writing, taper the height from start to finish - all sorts of bells and whistles !

A far cry from my first Calcomp drum plotter driven by CP/M where not only did I have to define the fonts, I had to write the program (a poor mans Autocad),in assembler, so that I cold submit plans drawn on it for my last workshop. It all worked but the planning officer thought I was mad (probably right!) - every rafter and joist was drawn. The building tapered to make the most of the space available, and I kept a constant pitch two facet roof with a sloping ridge so each rafter and joist was different !

Andrew
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East Sussex

Offline philf

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Re: Diamond Drag Engraver
« Reply #7 on: December 13, 2013, 09:24:33 AM »
Andrew,

What size is the Dremel diamond tool. As you say it's the cheapest.

I need to replace the diamond in my drag engraver and the tool is 3/16" dia. x approx 30mm long. I chipped mine when I made a mistake and ran out of spring travel.

Mine uses a piece of 12mm brass rod with a reamed hole for the tool. A 1/8" BSP grub screw provides adjustable preload.





I use Vectric Cut2D which will engrave any font. For TT fonts it just engraves the outline.

This was a trial for a trophy shield I engraved. It was done in Times New Roman.



 :beer:

Phil.
« Last Edit: July 13, 2017, 01:58:25 PM by philf »
Phil Fern
Location: Marple, Cheshire

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #8 on: December 13, 2013, 09:35:30 AM »
Not very different is it!

I wanted to be able to adjust the pre-load without removing the tool and changing the effective tool length hence front adjustment.

The Dremel diamond is very slightly under 1/8" - mine is in an 1/8" hole locked in place by a 6 BA screw in a collar (as the armature hasn't enough meat in it for a thread)

Andrew
Andrew Mawson
East Sussex

Offline Meldonmech

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Re: Diamond Drag Engraver
« Reply #9 on: December 13, 2013, 11:54:20 AM »
Hi Andrew,
                     Your lettering looks well. Incidentally I have machined a number of items from rebar, and been surprised how well they turned out. 
                                Cheers  David

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #10 on: December 13, 2013, 12:38:00 PM »
Thanks David, yes I was pleased how it came out as it was a spur of the moment mini project

I have a Mk2 on the drawing board , envelope, in my grey cells   :scratch:

Andrew
Andrew Mawson
East Sussex

Offline Doc

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Re: Diamond Drag Engraver
« Reply #11 on: December 15, 2013, 10:14:39 AM »
Good job I need to try this. The engraving look nice!
I know what you mean about the post I also use FeatureCam and have tweaked a post for my machine to get it to spit out the code I needed and it took a lot of trial and error to finally get it right.
Nice work!

Offline raynerd

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Re: Diamond Drag Engraver
« Reply #12 on: December 15, 2013, 10:40:40 AM »
Nice work, I made one a few years back and I was blown away with how well it worked. In all honesty, I'd never head of them even when I was trying to engrave text on my CNC machine! I showed what I'd done with a rotary tool and someone mentioned a drag engraver....


Offline awemawson

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Re: Diamond Drag Engraver
« Reply #13 on: December 15, 2013, 10:45:20 AM »
Thanks for the kind words DOC,

It's the arcane syntax that XBUILD (FeatureCAM's post processor writer) uses that gets me. This is the line I had to insert in the program start, and tool change areas

<IF>[le(<SPEED> , 49)]<THEN> [:<SPINDLE> = "5"] <ENDIF> <EOB>

Simple stuff but remembering the syntax always trips me up as I only fiddle with it once in a while.

Andrew
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Offline awemawson

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Re: Diamond Drag Engraver
« Reply #14 on: December 15, 2013, 10:46:40 AM »
Chris, it was your posting on this that entered a drag engraver onto my 'To Do' list, so it's all your fault  :lol:

Andrew
Andrew Mawson
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Offline awemawson

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Re: Diamond Drag Engraver
« Reply #15 on: December 18, 2013, 05:23:24 AM »
Well as intimated earlier I had an idea for reducing the side play so that fine engraving would be better. JS had suggested rectangular linear bearings but I wanted to stick with simple collet mounting. I found a 3/8" circular linear bearing sold by Marchant Dice, ordered up some 3/8" silver steel and put them together thus:

Andrew Mawson
East Sussex

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #16 on: December 18, 2013, 05:27:07 AM »
Compared with the Mk1 version it was somewhat shorter due to the length of the linear bearing, however as the silver steel was on the upper limit of tolerance (very marginally over 0.375 by maybe one or two tenths) there was no perceptible side play and a little pre-load on the balls in the linear bearing.

Andrew Mawson
East Sussex

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #17 on: December 18, 2013, 05:31:22 AM »
So what was the result. Well perfectly acceptable engraving  :ddb:

When I made up those EDM clamps from 304 stainless the other week, it was too hard to stamp with my Pryor letter stamps - I usually stamp my initials and date when I make something. Hence wanting the diamond drag engraver. So here is one finished engraved:
« Last Edit: December 18, 2013, 05:03:27 PM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: Diamond Drag Engraver
« Reply #18 on: December 18, 2013, 05:36:33 AM »
That lettering is about 4mm high. While I've been typing this post the machine has engraved the other nine clamps, with me popping up and down changing bits in the vice .

Andrew
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Offline John Stevenson

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Re: Diamond Drag Engraver
« Reply #19 on: December 18, 2013, 07:46:22 AM »
Very nice Andrew.

Another thought is that Igus do these bearings with a polymer coating instead of balls and for short movements it's probably better than the balls which over a period of time will groove the silver steel.

I know RS do the 12mm ones, don't know what other choices are out there ?
John Stevenson