The 3D Pantograph Club, Part 2: Jon’s Machine.

3D Pantograph built by Jon Tremlett.

The Pantograph, finished and installed.

In the previous post you will have read my story about a 3D scaling pantograph built by my sculptor friend Ed. As I also mentioned, my and Ed’s friendship started after we realising we shared a passion for motorcycles and an interest in these rather esoteric sounding pantograph things. So in this post I’ll shed some light on how it all came about.

The 3D pantograph, pictured above and covered in this post is a machine I built for a young artist a few years ago after being recommended for the work by another modelmaker. It is in some ways quite different to the one built by Ed, though in others it shares many similarities. There are no given set formats for these machines and so each is a direct response to a brief from the person who’s going to employ it. In my case the machine was to be wall mounted and capable of achieving quite a high level of accuracy, with variable scaling ability anywhere from 2:1 to 4:1. The artist sculpted in clay so no cutting actions needed, purely surface finding. As a consequence, this variability and need for precision dictated many of the design and fabrication decisions taken during construction, not forgetting the ever present need to work within a tight budget.

Cheverton Pantograph at soulcraftcandy.

The Cheverton pantograph used for reproducing scaled sculptures in alabaster.

To be honest I had never heard of a 3D pantograph when the job first landed in front of me, but all became clear as I took to the internet and arranged to go and visit one, currently residing in the archival warehouse of the Science Museum here in London. This particular machine was known as the Cheverton pantograph, named after the victorian industrialist who designed it for the manufacture of carved alabaster busts from scale models. It is a beautiful machine, quite a bit smaller than I imagined and a great example of a style of engineering design, lots of architectural references, so loved by the victorians. I freely admit that this machine heavily influenced my design, though it must be said that aside from some mentions of odd machines in America and Italy there is very little out there for the budding pantograph builder to study in order to construct their own. The Cheverton machine showed very clearly the pivoting arm for scaling pointer mounting, the different length pointers for achieving correct scaling and most important of all, a compact system for creating the two rotating turntables that enable the sculptor to access all points around a form.

3D pantograph by Jon Tremlett

The first iteration in the studio showing basic scaling function.

The image above shows the very first iteration of the machine temporarily installed in the artists studio. You can gather roughly how it works from the position of the two pointers relative to the positions of the two eagle sculptures positioned on the boxes. This was very much a prove out exercise, to make sure we were on the right track and to confirm some aspects of the geometry whilst I was building the rotating table structures. Because there was little or no documentation covering the detailed design of these things, it was quite a challenge to work out the exact geometry which governs how the machine works, and thus achieve the level of accuracy demanded by the artist. We encountered many problems to start with but overcame them once we’d realised what was going on. The essential premise is this: Firstly, the exact centre of the ball joint at the root of the moving boom needs to be on exacly the same line as the centres of the two scaling pivot joints. These three positions must be aligned by a straight line in space. Secondly, another straight line must pass through this ball joint and the two tips of the pivoting pointers. And finally, this latter line must also pass through two points at the centres of the tops of both of the rotating turntables. Simple enough you’d think, but a devil to work out without prior knowledge.

3D pantograph components by Jon Tremlett

The main pivoting components made using machined scaffolding parts and a lot of aluminium.

The scaling function of the machine is achieved through the relative positions of the pointer pivots along the main boom. For example, if the scale required is 3:1, then the second pivot would be three times further from the ball joint than the first. So if the first is say 500mm from the ball, then the second would be 1500mm from the ball joint. The pointers are also of different lengths in accordance with the selected ratio and correspondingly, the relative positions of the turntable centres needs to adhere to these spacings too. This means that for a machine like this, where an infinite degree of variability was requested (anything between 2:1 and 5:1), everything needed to be adjustable and lockable. Hence the pivots slide along the boom, the pointers slide through the pivot blocks, the turntables slide along their guide rails and finally, the chain drive that connects the turntables, which must turn in unison, expands or contracts in order to maintain chain tension across varying distances.

Rather than plough on endlessly, I’ll leave you today with some captioned photographs of the build which I hope will serve to fill in some of the background. Sadly I don’t have any more recent pictures, the machine was moved when the artist changed the location of his studio and I haven’t managed to gain access yet. I will keep trying though.

3D pantograph detail by Jon Tremlett.

Detail shot of the short first pointer locating small turntable centre.

 

3D pantograph detail by Jon Tremlett at soulcraftcandy.

Turntables, rails and chain drive under construction.

3D pantograph details by Jon Tremlett at soulcraftcandy.
Detail of the chain drive using proprietary bicycle components.

3D pantograph details by Jon Tremlett at soulcraftcandy.
The complete turntable and chain drive assembly ready to be installed.

 

 

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A return to the bike build.

 

 

Minimal fuel tank!

In the last installment of the bike build, which was let’s face it, too long ago and must be wrapped up soon, the exhaust was coming together. In order for me to be able to hear the results as the pipe came together a small tupperware container got a makeshift outlet fitted into its base and was then mounted to the main frame spar with a cable tie. With a bit of fuel onboard the engine could be started and run without the fuel tank in place and the exhaust listened to. The tank meanwhile was being prepped for painting.

The “silencer” that had been ordered came with an internal baffle already, if that’s what you could call it. You see these pipes everywhere on custom modified bikes so it will come as no surprise to anyone who’s ever had one that internally they are rudimentary to say the least. There was a piece of glass fibre packing inside the pipe but this was as good as useless. It would have disintegrated if you’d held it behind you and broken wind, frankly. So, first job was to get some proper packing material and firmly wrap the baffle so at least some of the noise could be absorbed. It was still too loud.

After a quick discussion about exhausts with the guys who’s workshop I was borrowing it was decided that the best thing to do was make a smaller secondary baffle that would fit into the end of the main pipe. Reckoning that the area of the holes in the internal cylinder should match that of the outlet it was time to have a go with the MIG welder. Not having used one much before, a quick session on the net provided some basic guidance to supplement the rather sketchy instructions contained in the user manual.

So a few hours later we had a finished baffle piece that fitted into the end of the main one that could be secured with three self tapping screws. Easy to remove and modify if need be and pretty much hidden behind the reverse cone end cap of the silencer. A couple of coats of aerosol heat resistant paint and the job was a good ‘un. This made a real difference to the sound and would be easy to remove if greater fruitiness from the pipe was wanted.This was the last fabrication job to do before the final build. What was up next was the biggest job of all, painting the bodywork.

 

Before moving on to that episode here are a couple of thoughts about MIG welding. Never having done any before, the thought of using the welder was a little daunting. Welding in all its forms has always come across as a bit of a black art, a deeply skillful craft practiced by wizards of metalwork with years and years of experience. This is all true but, it is also not as scary as it would seem. They say that every journey starts with the first step and so it is with MIG welding. Taking the plunge and having a go can lead you, with patience and concentration, to a thoroughly satisfying learning experience and hopefully a new found skill, and a finished part that you can be proud of.

 

My own introduction to this skill took me from making a simple baffle on the first day to knocking up a small paddock stand for the bike, to use during routine maintenance as I’d seen fit to remove the centre stand as part of the weight loss program. All within a week.

 

As mentioned before the manual that came with the welder was a little thin and searching the internet for tips and tricks threw up some really useful information and some tips which I never would have considered in my inexperience. Here are a couple of links to the two most useful websites found. The first one was the best: Firstly Tips and tricks and the second one here. Sadly the need for welding anything in my everyday work is rare but it hasn’t stopped me from wanting to buy a welder and start making something.

 

Although my skills remain relatively basic I’m no longer reluctant to consider using a welder for smaller jobs. Welding bike frames is something best left to experts for now but, with a new skill in the back pocket, the options available when making more complex ancillary parts has now grown and that can only be a good thing for when the next project comes along.

 

The welder used was a small portable unit with up to 150W of power, switchable. It had a variable speed wire feed, a small remote gas bottle (Carbon Dioxide/Argon mix worked best) and nice hefty earthing clamp.