Increasing The Bed Size
Last Updated: 27th June 2009
Why make it bigger?
The fact is that I would have liked a larger capacity laser cutter but couldn't justify the extra cost and, more importantly for me, the extra space it would take up. The HX40A, with it's stated capacity of 210x205mm, has a footprint of 810x510mm whereas the next model up, with it's 300x400mm bed, has a footprint of 1100x700mm. It's not a huge difference but when the beast has to live in your front room...
There are 3 reasons I wanted a bigger bed:
1. So I can cut bigger things (well duh!), however this isn't really an issue for me because pretty much everything I anticipate wanting to make, falls well within the specification limits.
2. The small bed size means that most raw materials that I can buy will not fit directly onto it and have to be cut up using a saw so I can fit them into the cutter.
3. When I want multiple copies of something, the small sheet bed size necessitates more time spent loading and unloading material, and less time with my feet up enjoying a nice cup of tea while the laser cutter does it's thing.
The really frustrating thing to me was that when I looked into the machine I observed that the cutting area was only a relatively small area within the main compartment. The main compartment is just over 500mm wide and 380mm from the front to the area sectioned off by the compartment that holds the laser tube. I also observed that the cutting head could move over larger area than the stated 210x205mm. Surly, I thought, there must be a way to expand the cutting area?
Why is it only 210x205mm?
The HX40A is generally described as an engraving machine and is clearly designed so you can put 'chunky' objects into the recess for engraving. My machine also came with a panel of metal honeycomb that can be inserted in that recess to support sheet materials. Incidentally the honeycombed portion of that panel is only about 170x190mm so if you want to cut sheets materials on the honeycomb, that's your limit.
The cutting head is capable of moving beyond the limits of the recess, however because of the height of the head, the beam cannot be focussed onto those areas. The image above shows the honeycomb panel set at the correct height for cutting 1mm sheet and as you can see, it's below the level of the blue/white surface. Achieving focus outside the recess would require that the blue/white surface be lowered, or that the head, mirrors and laser tube are raised.
Lowering the blue/white surface is not really an option because the sides of the recess are bounded by a couple of pieces of aluminium extrusion, part of the mechanisms framework, and either side of those are the drive belts that provide movement from front to back.
Raising the head, mirrors and laser tube would be easier however the amount they can be raised is limited (before the cutting head fouls the top of the case near the front of the machine).
An important consideration however is that either of the above ideas would result in the blue/white surface being only a short distance below the point of focus and, as it's plastic, would undoubtedly result in it being damaged by the laser beam passing through any material being cut.
Coming back to the question of why the stated working area is only 210x205mm, I honestly can't work it out how they've arrived at those figures.
As we've seen, we can't get focus outside of the recess, however the recess is 225mm wide and the cutting head can traverse the full with of it. It can't get right to the front because of the motor and spindle controlling movement from front to back, but it can go a little beyond it at the back. I reckon it can go 225mm from front to back as well as from side to side.
So that's a somewhat tight 225mm square but it doesn't allow for the fact that screws on which the height adjustable platform moves. They fall within this area at the back. So is the 210x205 the space allowing for the screws? I'm afraid not, because the width between them is only about 170mm.
Confused? I know I am.
I think what they're saying is that if you have an item measuring less than 210x205mm you should have no problem fitting it into the machine. However from experience I can tell you that if it's a little longer or wider then it MIGHT fit if it's also shorter/narrower. I have found for example that I can fit a piece of material measuring 166x250mm into the machine and this is useful to me because I have a convenient source for 1mm MDF in 250x500mm sheets, which can be cut into 3 sheets measuring 166x250mm. This fits between the screws and I can machine the full width, however I can't machine the full length. I can however cut things out of one half and then spin it around. Obviously it would be nicer if I could machine the whole thing without having to do this.
Why not just buy different sized raw materials?
Given that a big part of my problem is the work needed to cut sheets of raw material to a size that will fit into the machine, you may be wondering why I don't just buy a different sized sheets. Sorry if the answer to this is obvious to you, but for the benefit of those to whom it isn't:
The best value way to buy raw materials is to buy the size in which it's manufactured. If you want it smaller then somebody has to spend time cutting it up, and that adds to the cost.
In the past I used to buy and sell craft foam. The manufacturer made it in 1200x2400 sheets and I used to sell 300x400 and 200x300 sheets to model makers. However I bought the foam in 600x600 sheets because I couldn't handle the big sheets and couldn't justify the cost of getting my supplier to cut them to the exact sizes that I wanted. The compromise was to get them to cut the big sheets into 600x600 squares and I did the rest.
Plan A - 300x400mm
The next laser machine up in the range has a 300x400mm bed while the next one after that is 400x600mm. It's my understanding that these dimensions have been chosen because they would allow a 1200x2400 sheet of material (a fairly standard size) to be cut down into an integer number of smaller sheets for the machine. Given the internal dimensions of the cabinet I speculated that it might be possible to squeeze a 300x400 bed inside. What's more, I initially thought that I would be able to do it while making use of many of the existing parts. Unfortunately the more I researched the possibility, the more and more parts got added to my list of things that would need replacing.
The current arrangement cannot achieve 300mm of movement from front to back so I considered turning the orientation of the mechanisms though ninety degrees. This would mean that beam upon which the cutting head moves could be shortened and re-used along with most parts associated with it. It would however need new 'brackets' for the ends of that beam in order to get 300mm of travel for the head in only 380mm of space in the cabinet.
It would also require the use of an additional mirror (for which I'd need to make a mount), and longer drive belts. Alas the existing belts have a 2mm pitch and as I couldn't find a source for longer belts with that pitch I concluded that I would have to replace them with 2.5mm pitch belts and replace the pulleys too.
Add in the aluminium extrusions required to make a new frame, new mirror mount for the end of the beam, and a few other bits and pieces that would be needed in order to squeeze 300mm worth of cutting distance from front to back of the machine, and I began to have serious reservations about whether it was really worthwhile. The fact is that I don't have a source for 1200x2400mm sheets of materials nor the facilities to cut them down to 300x400mm if I did. In fact the 500x250mm sheets to which I do have access are quite convenient and I have a Proxxon Bench Saw that I can use to cut them into three.
I decided to take a step back from the idea of trying to convert the machine to handle 300x400 and see what might be achieved without such major modifications.
Plan B.1 (Width)
The recessed area is 225mm wide and, as shown by an earlier image, has what looks like a piece of rectangular section tube running from front to back along each side. Upon closer examination that box section is part of a more complex extrusion which incorporates other important elements. Increasing the width of that recess would therefore be quite a task and, I think, takes us into the territory where we might as well revert to plan A. Within the recess we are further limited by the presence of the screws that support the rise/fall bed. Now if these could be moved, removed or modified...
Moving the screws would be difficult, as would replacing them with a different mechanism (a scissor action device perhaps), however, as I am generally working with sheet materials from about 0.5mm to 3mm in thickness so it occurred to me that I could replace the rise/fall bed entirely, with a fixed bed set at the correct height for 3mm material (allowing for a honeycomb or pin-bed to sit on top). For material of less than 3mm I would then need to insert a packing sheet under the honeycomb/pin-bed to raise it up a bit.
Another option would be to shorten those screws to a length that would allow 1-3mm material to go onto the table without them interfering.
Doing this would mean that I could fit A4 sheets of material into the recess. I couldn't machine the full length, but I could at least get it in there and machine the full width. A4 is of course a common size for raw materials at art, craft, and model shops.
I also considered that I could probably make and insert a new fixed bed such that it could be lifted out, and the old one popped back in again, should I ever need it.
Plan B.2 (Length)
With the height adjustable bed's screws out of the way I'd have close on 225mm of length as well as width. Tantalisingly close to the length of my 166x250mm MDF sheets.
The closest we can cut to the front of the machine is apparently determined by the maximum travel of the mechanism carrying the cutting head. However this is actually cut short by a 30mm long plastic spacer attached to the round rod on which the right hand side of the mechanism moves. After some considerable measuring and thought I concluded that this could be shortened to 20mm to give us an additional 10mm of travel. (See later in this article for a photo of my modified version.)
At the back we are limited by the compartment containing the laser tube. However the head stops about 15mm short of this. Interestingly, there appears to be another 25mm of travel available, or at least there would be if the home position sensor were modified. The sensor itself is mounted on a little circuit board and is triggered by a piece of angled metal (see photo). I couldn't see any reason why this piece of metal could not be shortened to allow a little extra travel. However this became a moot point when I removed this sensor entirely in the process of converting my laser cutter to use Mach 3.
Plan C
While mulling over and measuring things for Plan B, I started thinking about swapping the cutting head to the other side of the beam along which it moves, and maybe moving the motors and drive shaft to the back of the machine. In other words: it occurred to me that the limiting factors in relation to the travel from front to back might be overcome by rotating the bed through 180°. I took it out and spun it around to see how it might work:
The height adjustable bit is not in place and the 2nd mirror has been removed from the end of the beam. This 2nd mirror would have to be moved to the opposite end of the beam and a new mounting bracket would be required.
It was necessary to remove the metal ducting for the extractor from the back of the machine in order to get the 'innards' into this position. I would need to create a new duct to work around the stuff that is now in the way however this could be done in conjunction with my idea about air assist/fume extraction.
New holes would have to be made in the base of the machine to mount all of this stuff. There are also a couple of holes in the back of the machine to give access to the tensioning screws for the front-to-back drive belts. New holes would need to be made in the front of the machine for this purpose.
The wires ARE already long enough. Yippee!
This arrangement would allow the head to move a gnat's whisker over 250mm from front to back in the recessed area. Thus it would allow me to machine the entire surface of my 166x250mm MDF sheets.
So what did I do?
The more I looked into Plan A the harder it seemed to achieve and ultimately the balance of benefits versus difficulty got tipped decisively in favour of "don't bother".
Plan C is really only recorded here for the benefit of readers who might be wondering "what if...". Plan C offers nothing that cannot be achieved much more easily with Plan B.
Plan B, I concluded, would give me a lot of benefits for very little work and with the home sensor removed as part of my conversion to using Mach 3, the only remaining step to achieve part B.2 of the plan was to shorten the white spacer. This was simple enough once I'd disassembled the bed but if you plan to do this yourself, here's a tip: Removing the spacer intact necessitates taking the bed to pieces. I'd done that anyway in order to assess the other possibilities but if all you want to do is shorten that spacer then I suggest that you just cut/destroy it and replace it with a 20mm length of split tube held in place with a cable tie. The image below shows my shortened spacer and, at the other side, the thing that really imposes a limit: a notch in the track.
I now have just over 260mm of usable space from front to back. I haven't yet implemented part B.1 of the plan but that will happen real soon when I make a pin bed.