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CNC engraving

Spring loaded engraving tools

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IanH04/10/2009 22:12:24
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129 forum posts
72 photos
I have been exploring CNC engraving on my Denford Easimill and have made myself a spring loaded tool holder. This is essentially a spring loaded mounting for the Axminster Power Tool centre heavy duty flexible drive which I found a recommendation for as a sounrce of a few tens of thousand rpm.
 
I am using 1/8" dia shank engraving tools sourced from Ebay and would like to get  an idea of how strong the spring should be. I read the MEW article on a spring loaded tool holder for engraving but it did not give an indication of the strength of the spring.
 
Anyone got any ideas?
 
I will put anexample of some engraving in amongst my photos.....
 
Ian
Paul Boscott05/10/2009 13:33:38
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99 forum posts
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Ian
Looking at your photo I would not have recommended a spring loaded tool holder for that job.

My understanding is that a spring loaded tool is used when the surface that you are engraving on is not flat or not planer so that the pressure of the spring provides a constant depth of cut over the contoured surface.

Paul Boscott

Bob06/10/2009 17:25:45
51 forum posts
1 photos
Hi Ian
 
I think Paul is right about the spring loaded engraving tool. I think their main use is for manufacture of prototype PCBs from copper coated circuit board using island isolation milling to create the tracks. The material is very difficult to hold down flat and as the engraving is only about 10 thou deep the irregular surface results in erratic results if a normal engravint tool is used.
 
Bob
IanH06/10/2009 21:55:01
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129 forum posts
72 photos
Hi Paul and Bob,
 
Thanks for your thoughts. The thin brass I used for the dash board badge was clamped down onto a piece of wood which gave a somewhat eneven surface - I had three passes at engraving it getting down to about 10 thou in total from memory. The first pass was a bit hit and miss as the brass was not completely flat, partly as a result of the clamping method and partly as a result of it being cut out of a bigger sheet with snips. Note that this was with a tool in the normal spindle. Going to a spring loaded tool was hopefully going to allow me to get the engraving done in one pass.
 
Have a look here to see a commercial offering http://www.2linc.com/engraving.htm 
 
I had a go with my spring loaded tool on the end of a reproduction Best and Lloyd oil pump plunger - the "happy man" logo has to go onto a domed knob. I was not confident enough to set the cut depth to .1" say and let the took find its own depth as it traversed across the domed surface.
 
Have you any feel for whether the spring should be "strong" or whether I should be able to lift the tool with one finger for example? Perhpas I have to just risk an engraving tool and "suck it and see".
 
Ian
 
 
Paul Boscott07/10/2009 18:09:00
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99 forum posts
21 photos

This was my solution

I wanted to engrave glass that has an uneven surface but at the same depth over the length of the text. After a few failures I came up with this solution A sprung loaded collet chuck to take the collets and tools from my dremel

The thread on the front of the dremel is 9/32 x 40 a standard M.E thread I was able to buy a die from RDG tools. The next experimentation was the force of the spring I am now using one extracted from a plastic ball point pen. The tool bit is a diamond impregnated ball 1.5 mm Dia in a 3mm shaft.

My contribution to safety was to put a copper shield around the drive pin as the tool rotates at 5000 rpm if it were to come out you can bet that of the 360 deg range it would have to chose from it would aim straight for your eye.
 
For drawimg see my photos
 
Paul Boscott
IanH09/10/2009 21:35:03
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129 forum posts
72 photos
Here is a vide of a commercial tool in action;
If you go to about 1.06 into the vide the operator moves the tool against the spring which gives me the impression that it is a pretty light spring.
 
Ian
IanH24/06/2010 21:45:58
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129 forum posts
72 photos
Just looking back at this post I thought it would add interest if I added a photo of an engraving project. This is a reproduction dash board badge made on the Denford that now adorns my Morgan.

This shows it after engraving (milling really) before painting.
Ian

Terryd24/06/2010 22:18:20
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1946 forum posts
179 photos
Hi Paul,
 
I noted that you said that you "clamped" down the brass sheet.  Why not use double sided tape to stick it onto mdf and clamp that down?   It should be quite flat then.  Double sided tape will withstand the cutting forces easily for this kind of work.
 
Terry
IanH25/06/2010 20:10:22
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129 forum posts
72 photos
Well, no good reason for not using doube sided tape really - I have used double sided tape in the dim and distant past on something or other but found it was less than happy with coolant around so I have not used it since. There was no coolant on this job of course but I didn't consider tape. I will remember this for next time.
 
Ian

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