View Full Version : Rotary engraving

Paul Proffitt
03-03-2007, 7:17 PM
It was suggested in another recent post on making a rotary tool jig that the diameter of the engraved object needs to be considered in relation to the diameter of the drive wheels on the Epilog rotary accessory for rotary engraving.

In the past I've actually measured this relationship by marking some blue tape on the object to be engraved with a grid pattern so that I could calculate the actual versus expected distance. I found that there was a very slight difference, but I've only done this test on one object. Not a definitive test.

It seems that if the laser driver is translating Y distance as circumferential distance on the drive wheels that the diameter of the engraved object should not matter. This would seem to be true of the driver knows the exact diameter of the drive wheels including the o-ring (assuming compression of the o-ring isn't a factor) so that it can then easily calculate the linear distance based on steps on the motor that drives the rotary tool.

If, however, the driver is ASSUMING the engraved object is the same diameter as the drive wheels then it must be equating Y distance to some angular movement of the wheel. In this case the ratio of the diameters of the drive wheels to the object to be engraved would have to be used to adjust the drawn Y distance measures in order to come out with an actual Y distance.

It seems to me that if there is just a slight, relatively constant discrepancy between the drawn and engraved Y distance it means that the driver's value of the drive wheel diameter is not exact or does not / can not take into account any compression of the o-ring which would effectively change the actual diameter and circumference.

Anyone have any insight or experience about what is actually going on?

Epilog Legend 24TT

Paul Proffitt
03-04-2007, 10:06 AM
Finding out that lots of forum posters here refer to 'rotary engraving' as something other than engraving a cylindrical object in a laser I thought a change of title might be useful.

Mike Hood
03-04-2007, 10:20 AM
Good idea. I think it's a really misunderstood topic.

Also... there are some very significant differences between the types of rotary fixtures ... and true rotary "engravers".

Roy Brewer
03-07-2007, 9:25 PM
engraving a cylindrical object in a laserPaul,

I often explain that the Epilog cylindrical attachment logically "flattens" the cylindrical object. Diameter is not relevant.

From your multiple choice question, the driver knows the diameter of the wheels, hence it "indexes" on the outside of the cylindrical item intercepting the normal Y axis movement.

Especially for "decorative" applications this works very well. However if it is necessary for your graphic to be proportional, some calculations may be necessary if you are "indexing" on a portion of your cylindrical that has one diameter and the location of the engraving had another diameter. Pretty simple stuff: what's the percentage difference? Then stretch/shrink your graphic that same percentage.