Like most of us I love a new gadget or tool and like most of us I have my fair share of those essential new tools that, frankly, end up in a drawer or cupboard and never see the light of day...sound familiar?
Well one of those things for me was the laser guide for the hollowing rig, a lot of people swear by them and I went ahead and got one with my hollowing rig. It certainly was useful but it was not the "silver bullet" that many had given the impression that it would be and it certainly did not prevent the production of hollow forms that were larger on the inside than they were on the outside....think about that one!!
The laser system is intended to allow you to "see" the wall thickness as you are hollowing a vessel. The laser pointer is held in a fixed position above the cutter with the beam set to your desired thickness and shining down onto the workpiece, the idea is that when the beam just drops off the outside profile you are at your thickness.
You can see the laser thickness system on the hollowing rig in an earlier article here.
So far so good then...I should now have no problems with thickness of walls and I should not be making any more of those Tardis hollow forms (bigger on the inside than the outside - get it!!).
Well not quite is the answer and here is why.
The laser "dot" is set at a distance measured in "mm" from a specific point on the carbide (or other) cutter and if you are cutting on that spot the measurement is accurate. For example if you are making a tube then you will be fine with a single setting of the pointer as you will always be cutting on one spot on the cutter.
However if you are making something with curves then you will be cutting on different parts of the cutter as you move around the shape you are hollowing. This means that the wall thickness you have set the laser "dot" for will not be accurate across the entire vessel and you will have to either stop and reset the pointer (can be a bit of a faff) or just kind of guess how far out the dot is at any given point in time....at which point we are back to Tardis hollow forms and flying shards of wood!!
So having seen folks using a camera system for a little while I decided on an upgrade, however most of the upgrades were well beyond anything in the pocket money range so a little creativity was needed. A quick scour of eBay gave a reasonably priced reversing camera which was purchased, the spare room gave up an old computer monitor (you see my Dad was right when he used to say "That might come in handy one day").
I was able to simply re-use the laser mounting arm by adding a scrap of wood with a couple of holes drilled in it and hey presto one camera hollowing guide was created, total cost was about £30 and to be honest most of that was spent on the bracket to wall mount the monitor.
So, setting up the camera for use is pretty much the same as the laser really, position it above the cutter (a bit of card under the cutter is a good idea) and then mark on the screen where the cutter is and draw a second line for your wall thickness. When the cutter is inside the vessel the two marks will be visible and show you where the cutter is and what wall thickness you are at regardless of where you are cutting.....easy!!
Well... like most things there are a few things to bear in mind.....
- Always use "dry wipe" markers if you are marking directly onto the screen. If you use permanent markers the marks are difficult to remove...don't ask!!
- The image on screen may well not be "to scale" so measuring on the screen for your wall thickness may lead to .... unexpected results...and we're back to Tardis hollow forms and flying shards of wood again.
I had a couple of goes at making a guage to get my wall thickness sorted, the first was a very "Heath Robinson" affair using lollipop sitcks which kind of worked but was a bit of a faff. The second attempt was using a circle of card with a hole in the centre for the cutter and an outer diameter measured to give me the wall thickness needed, this proved to be more successful! The cardboard has now been replaced with plywood and I have a set of these for different wall thicknesses.
So there you have it! A reliable way of getting your wall thickness regardless of shape.
Is it the end of Tardis hollow forms? Well most likely not but you can always dream....