Episode 120 Making the TT Rex

Material: 3mm Acrylic
Router Bit: Amana Tool 514411/16″ Spiral-o-Flute upcut from Toolstoday.com
CNC Router: Torque CNC 9060
Spindle Speed: 12000RPM
Horizontal Cutting Speed: 5mm/sec
Vertical Cutting Speed: 10mm/sec with ramping

Plans from MakeCNC.com

Garrawi

Cockatoo-2

The Trouble with Heat

One moment you are working away quite happily, the CNC is humming along and everything is just so.

The next, things are NQR – items are breaking loose, engravings are either too shallow or too deep, and the vacuum table is not doing its job.

It is the afternoon of a warm day, and the MDF spoilboard had suddenly started to warp and flex, pulling away from the vacuum table. It wasn’t something I had experienced with very thick MDF, but once the thickness had come down to around 8-12mm or so, it was a real problem.

I first thought the solution was easy – buy more 32mm thick MDF, after all, the first lot came from Bunnings.  But there was a problem.  That was apparently intro stock for the new store, but not something they were going to carry in the long run.

I got to thinking, and one thing that I had tried unsuccessfully, was to place a piece of 3mm MDF on top of the spoilboard (on top of the vacuum table). As a trial it was unsuccessful – to many losses in the system.  But what if I ditched the spoilboard altogether, what then?

So I milled the base really flat, (still a sacrificial piece), then instead of placing a spoilboard on top, I placed a simple sheet of 3mm MDF on top.  It is thin enough that air is drawn straight through it without having to mill off the heavily compressed portions top and bottom, and it is a very uniform thickness.  Also, rather than having to mill, and re-mill it flat as it gets chewed up, it can be flipped over and the other side used, or simply discarded and another $2 sheet bought in.

The other main drawcard of the 3mm spoilboard, is it is thin enough that the vacuum base pulls it flat whether it wants to tend to curve or not.

The first few runs really proved how effective it is.  Not only was the sheet being cut held down well, and very flat, there was significant vacuum that kept the pieces in place as they were cut free, and drove the dust deep into the cut groove.  This was packed rather tight, so the bits did not move even though no tabs were included, even when the entire board was picked up and turned over to sand the other side.

Small refinements to technique, as a result of an adverse situation.  Happy days.

Acrylic Snowman

While the MDF snowman worked out nicely, and it looked ok painted up, I wanted to get back to trying my hand at making some models from acrylic.

Given that Christmas is rapidly approaching, I thought I’d tackle the snowman again, and see just how well the CNC, along with a new set of router bits specifically for plastic from toolstoday.com would work out.

Just an aside for a second.  I have just gotten an iPad Pro, and while writing the article, have used one of the pro’s features of being able to run a second program simultaneously, and on screen at the same time.  Awesome feature! 

  
I also found a better supplier of plastic sheet goods, so that will be great (and dangerous to the wallet).  They also sell acrylic ‘glue’, and it is a vast improvement over using Superglue.

I still have some processes to work out to make things run smoother on the CNC process of working with acrylic, but for the most part it went very well.  Acrylic is pretty flexible when it gets thin, even worse than MDF it seems, if that is even possible.  So I found myself supervising the whole job while it was machining.  I was using an upcut bit, and perhaps that also has a lot to do with it.  While chip clearance is important (especially with a material that can melt), lifting the piece is not the best way of ensuring it is stable.  I still don’t have revolution speed control, so am still running the bits slower than I would like, and again that is probably a real factor.

Still, the result is a great snowman. Looks awesome (especially with Kara Rasmanis wielding her camera)  

 Next one to tackle – an acrylic AT-AT (Imperial Walker) in greys and black plastics. And there will be video, just once I have a better idea of just how to manage this material!

Death of a Vacuum

It was almost 4 months ago to the day, that I built a vacuum table for the CNC router.

While it worked well, I was sure the lack of overall airflow would result in the vacuum carking it very quickly.  Job after job, and it kept going.  It was encased in a rubbish bin with noise absorbing material stuffed around it to drop it’s horrendous noise down to bearable levels (it was a ShopVac, and it always was a screamer). It ran warm- the exhaust was always hotter than was healthy.

Went out to the shed tonight to check on a job, and although the CNC has indeed finished, it was a lot more silent than usual.

Instead of the muffled sound of the vacuum, there was a familiar smell of burnt plastic and ozone.

Carefully switching it off then unplugging it from the wall, I went on dealing with the job at hand, and then went over to the garbage bin, and started unpacking.  Partway down, and the normally white insulation material started coming out black.  Desite being some time, the vacuum itself was still very warm.  A complete meltdown.

Not as bad as the last vacuum though.  Years ago, I had a household vac for dust extraction, and it also failed in spectacular fashion, actually melting until it literally fell apart, and the motor fell out of the housing.

So the machining tonight has stopped, slightly prematurely.  I haven’t added up the hours the vac did in those 4 months, but it would legitimately be into the hundreds of hours.  Hundreds of hours, in a MDF laden atmosphere, with poor airflow. I think it did a pretty good job in the end!  Not even sure what the designed duty cycle of the vac was, or the model’s MTBF (mean time between failure).

So now the decision is “what next”?

Another cheap vac?  A vacuum pump?  If so, which one?  There’s a bunch on eBay, all different cfm, and I have no idea what cfm I’d actually need, let alone my current table would leak like a sieve, so would never actually be able to maintain a vacuum.  And that means the vacuum pump would be running continuously, unless I make some real mods (rebuild) to the table itself.  What do commercial machines do for a vacuum table, and the pump for them?  Too many questions, not enough answers (yet).

Miscellaneous meanderings

Had the annual hard rubbish collection for the area last week.  As always, it is an opportunity to get rid of a whole raft of things that have been clogging up the works.  In my case, it is often heavily made up of shed-generated rubbish, which more often than not, is the result of previous projects.

So the hard rubbish collection ends up briefly being a reliving of projects past.  This time it included a large pile of offcuts and waste from the CNC Router.  Sure have run some miles up on the router bits this year!

Speaking of which, opened the mail yesterday to a new collection of router bits I’d ordered from Toolstoday.com.  This set is the collection for plastic cutting as I have plans for some upcoming projects.

Screen Shot 2015-10-28 at 10.30.06 pm Screen Shot 2015-10-28 at 10.30.52 pm

An interesting video on the golden ratio, which is a commonly used ratio in creating aesthetically pleasing objects, such as box and furniture proportions.

And finally, a bit of a weekend woodworking project for someone….

Photo 29-10-2015, 00 43 57

Mass Construction

Things have been pretty full-on around here recently.

In addition to the standard fare, I have been really churning out things on the CNC.  Sheet after sheet of 3mm MDF getting turned to Swiss cheese as I make up small kits in time for a fundraising school fête this weekend.  There are now over 250 individual kits, all bagged up in zip-lock bags, with a set of instructions on assembly, and an assembled example model of each design ready to go on display.

I’m not selling them for much – $5 for many of the designs, with the larger ones being $7.50 or $10 as they really scale up.  The idea is to cover cost plus a bit for the fundraising, and still keep them affordable enough for primary school kids to afford.  With each kit taking on average 30 minutes to cut out, it means the CNC is cutting way below what you would normally calculate its hourly rate at, but that is not the intention for the weekend.

The designs I am using all come from MakeCNC.com.  It raises a question about copyright – this is not just taking someone else’s concept and producing your own equivalent to sell, in this case it is actually using their designs to produce something for sale.  It is actually covered as part of the contract you agree to when purchasing the MakeCNC design.  You are allowed under the condition of the purchase of the plans, to make up to 50 of each design and include a set of instructions with each.  Given that the Mega Collection I originally purchased has over 150 designs, that lets me make 7500 models for sale (if that is what I was looking to do) and still be complying with the copyright terms I agreed to.

While some (quite vocally) disregard CNC machining as being woodworking, that doesn’t bother me at all.  This is taking the workshop I have, and producing a product that is marketable (well I hope it is marketable – this weekend will be a good litmus test!) That is a fun concept in itself, and reinforces what I like to try to get my woodworking to be – cost neutral, at least as far as possible.

It is nothing more, or less, than a cottage industry, which is a throwback to the 17th and 18th centuries (which persisted until the mid 19th until it was really replaced by the industrial revolution).  I like that concept.  A small number of people (often one) working away in a niche market to produce quality goods.  In this day and age, when everything is made in vast quantities, in factories overseas, the fact there are some items still available produced individually and with particular attention to quality and detail has a lot of appeal.

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