Idea for a pantograph engraver.

[Brock Little]

Just thought I'd share an idea.
I was in a hardware store earlier today, and saw a monitor mounting bracket that gave me an idea for a piece of machinery I've been looking to build. I'd need to buy two of them, but don't be shocked by the price tag on the box, the price is in Hong Kong Dollars

I went home, and did up a quick sketch to help put things into perspective. Of course, the quick sketch turned into two hours of dicking around (I'm sure we've all been there). I'm liking the way it's shaping up, so I'm keen to get it together. Sadly, it won't be soon, because I'm starting another job this week.

It'd be good for fine detail work like inlays and fine lettering. As it is in the drawing, it's at a 2:1 ratio, which should be fine enough for my purposes. I'll have to do a bit of adjustment to some parts, but most of the work is already done. Either way, the main plus for me is the price! Let me know what you guys think.

Cheers
Brock

[Enzo]

Nowdays everything is CAD. Back when there were actual draftsmen, there were things like you envision for copying dringsns, and also for size reduction or enlargement.

Also look up "Leroy Lettering Set" for an interesting tool we all learned to use... long ago.


All those things are for drawing, but tracing a drawing to make an etch on the other surface should be an easy conversion.

[Brock Little]

I know what you mean, Enzo. I've been drafting for about twenty years, and prefer to do my work by hand, whenever possible. If I'm drawing something, and I know what the final result will be, then I often do it by hand, but if I know I'm going to need to do a lot of editing, then CAD is hundreds of times faster. As for lettering, I always did mine freehand. Stencils and lettering sets are for noobs :P
The machine itself won't be used so much for engraving. I'll mainly be using it for carving. It might not be obvious from the drawings, but it will be set up to accept a dremel or flex shaft tool.

B

[Mick Bailey]

A few years ago I did some development work with a Canadian engineer who was designing and prototyping a pantograph engraver that would also 'carve' relief objects in 3D as well as carry out regular text engraving. The idea was to be able to reduce or enlarge the subject.

The challenges in doing this were (are) considerable. X-Y is fine, but maintaining geometric accuracy and linearity at the same time in a Z-axis is tricky and the machine ended up being considerably more involved than initially anticipated.

I also have a Gravograph commercial pantograph engraver. Very precise, rigid and accurate. Over the years there have been a number of successful DIY machines based on this, or the Taylor Hobson machines.

The first though that struck me was how much play/backlash would there be in the mechanism? Play means distortion in the finished object, lack of ability to capture detail and vibration in the tool.

My next though was how you'd articulate the cutter and tracing arm in a vertical plane. With commercial machines you can locate the tracing arm without the cutter contacting the workpiece, in order to get the cutter located above where the cut is to start. A crude way of doing this would be to hinge the entire pantograph assembly and pre-set the cutter depth in relation to the tracing stylus. The downside I've discovered with this approach (especially problematic with 3D) is all the cutting geometry is determined by the radius struck form the hinge point, and this radius varies with the cutter proximity to the hinge. Not a problem if all the engraving is done on an X-Y plane and the pantograph always operates parallel to that plane.

[ric]

Mick raises some good points. Slop and how you might need to adjust it out was my first thought. I made an old worn wah have a firm smooth action by drilling in and tapping for set screws. They make set screws with nylon or similar tips, those might be an option.

I've seen vertical axis accommodated with the entire mechanism sliding on sleeves on four corner posts. This limits the size of what can be cut. For ideas on that type slide you might look at a slide chop saw as used by carpenters.

[Brock Little]

Some good points, Mick. My main concern with the intended use of something like this mounting bracket wasn't slop, but the adjustability of the joint tension. These brackets are typically very firm, and are actually designed not to move. I pulled the parts out of the box to check them out, and not only are they adjustable, they also had nylon bushings and no play, even when loosened. If it turns out I'm getting a bit of play in the mechanism, I'll start by adding another tier to the single bar section.
The lowering of the tool is easily handled by a retractable central pin through the stylus, so that the cutter head can be lowered once the pin is centred over the template. I'm not so worried about vertical variance as the range of operation will be between 0.5 - 5mm for my purposes. I anticipate that the human element would be a greater concern. Either way, the majority of my uses for it will be in 2D with very little vertical variability once operating.
Mick, I'd love to see some pics of the Gravograph, if you've got any to share.
Thanks for the input

B

[Mick Bailey]

Here are a few pics - let me know if there's anything specific you'd like me to photograph. You can see how the tracer arm is hinged to allow initial positioning on the copy slide. The cutter arm requires light hand pressure to bring it into contact with the workpiece.

Every action is balanced and smooth so that the nuances of the subject can be traced accurately. I use the machine for panel lettering, logos and for cutting out shapes in thin material. I also engrave serial numbers using a static diamond point instead of the rotary cutter. In addition to the commercial type blocks, I make up custom graphics fretted out of thin sheet brass stuck to a sheet aluminium base. This makes a permanent design that can be repeatedly used - just trace around the outline.

[Brock Little]

Nice machine! I love old tools and machinery. So, this is an actual engraving machine with preset depth and push for the cutter to initialise. The one I'm planning more closely resembles a carving machine than an engraver, I guess. There's no hassle for me to set a depth stop for when the cutter is engaged. I plan to use pathing templates, rather than scale templates. You can see what I'll be using it for via the FB link below. Thanks, Mick.

B

[tedmich]

most modern CNC routers include a sensor probe which can be drawn over 3D objects to encode cad files, then infinite copies can be made. Some have very fine resolution. There are optical readers too, with hacked Xbox Kinects working in some apps. A direct mechanically coupled pantograph would also likely benefit from machine controlled input in regular linear paths rather than manual nonlinear input. Also think about non homogeneous media like wood, gotta think about directionality when cutting something with a grain!

[Brock Little]

Well, it looks like my original plan has to go in the bin. I may still build a small pantograph, but the bracket I had my eye on isn't going to work. The plan was to use two of them, and fix them together, but... The first one I pulled out of the box to check last time was great, but the second one was completely different. One was made from welded hollow section, and had nylon bushings in the joints, the second one, while having identical dimensions, was made of solid cast material, and had no nylon bushings, sloppy joints, and was altogether useless. A very big difference from one batch to the next. At least I didn't have to buy them to find out.

I have considered doing some things by CNC down the track, but I won't need a scanner of any kind. Thanks all the same, Ted CAD drawing and data processing are kind of second nature to me. Unless I get ambitious, and decide to build my own CNC... Don't tempt me! I'll be working mostly with homogeneous materials, plastics etc, so grain direction is rarely a problem for me.

After a disappointing start to my day, I ended up in another shop where I found what I'd been looking for all along! For quick reproduction of small parts, I'm now looking at re-purposing a key cutting machine. I'm looking into tooling speeds to see if they'll work for my purposes, but it's looking good. I shouldn't need to do more than modify the work clamping area. Let's see if Mrs. L will let me buy another machine...

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[Rick Turner]

If you can do the CAD, there are a whole lot of shops that can CNC rout, CNC mill, 3D print, or CNC laser cut anything you need. We sent out files for pickup bobbins to be laser cut. They came back perfect. We sent out files to be 3D printed. They came back perfect. The questions you have to ask yourself are: How many parts do you need to make? Can I justify and amortize the cost of a machine and/or the time to build it within a reasonable time selling my products? Or...am I a hobbyist who just wants to fiddle with machines and not sell any products for a profit? There's a time to make "in-house"...early on, prototypes, etc. Then there's a time to sub-out...first runs of limited production on into fairly serious. Then there's a time to bring it back in-house...when you can keep your capital investment in tooling busy.

[Rick Turner]

Also, I find it kind of hard to believe that an experienced CAD guy would want template guided hand operated gear! Unless it's a hobby... It's certainly no way to make a living at this stuff.

[Brock Little]

Hi Rick. It's hard to believe, until you know that some of the materials I work with will be outright refused by any CNC workshop. I'm getting a lot of people take an interest in the horn products I produce, and it presents a lot of problems for automation. Irregular materials that need to be individually aligned for grain direction and clamped before processing. Then the end product still needs a lot of hand finishing anyway. The whole exercise wouldn't save me any time or money per unit.
All this aside from the fact that cutting horn smells like burnt hair and toe jam. Then someone decides to hose out the workshop (cause that's got to stop the stink, and settle the dust, right?), and it then needs to be evacuated, because the stench is now unbearable.

I've just ordered some laser cut acrylic blank stock of about 200 pieces, and I'm very happy with the cost, but there's still a lot of hand work to do. Very excited to pick these up! I have access to a 3d printer, and it's ok for prototyping, but it doesn't produce a finished product.

I'm looking at doing custom pickup bobbins in bone and other natural materials in future, but here are some of the things I'm producing now.

Cheers
B