Maximising Yield – the Vacuum Table Story

For months I have been bantering around the idea of a vacuum table for the CNC router, but each time decided that screws or pins were easy enough, and the whole issue stayed in the too-hard basket.

As I have been doing quite a bit of nesting work recently, it gave me pause to thought – for a one-off, a few screws are all very well, but the combination of that, and the significant time wasting of using tabs to restrain the cut components (both drawing them, and then physically having to cut and remove them) was proving an incredible time waster.

So I finally was pushed into addressing the whole material hold-down issue.

I started doing a bit of research online, but the results were less than helpful, and I felt as a whole, a lot more complicated than necessary.  So instead, I decided to build an idea I had, and just see if it worked.

I did use the CNC for the following steps, but that is certainly not necessary, and secondly, while I am using this on the CNC router, there is absolutely no reason this cannot now be applied to other areas of woodworking.  Nor do I expect I have come up with anything novel, but in going back to first principles, hopefully I have significantly simplified the solution.

So to start, I took a thick piece of MDF (22mm or so, which I had to hand.  I would have used thicker, but the 32mm MDF I bought last time from Bunnies was only some of their promotional stock.  Not sure what they were promoting, because they don’t stock it otherwise).  With a 1/2″ ball nose router bit, I cut a matrix of tracks, 5mm deep, and about 20mm apart, both horizontally and vertically, stopping about 10mm from the edge.

Next, the edges of this board were sealed.  I know people use some edge tape, or shellac for this, but I thought PVA glue would suffice!

This board was then screwed down to the bed of the CNC machine, and a hole just big enough for the end of a vacuum hose was drilled, all the way down and right through the table.  The hose of the vacuum (connected up to a cyclone separator) was jammed into this hole from underneath.

A second thick board of MDF was laid on top of this bed, and the vacuum switched on.

Test one – does it suck? Yes it can! The first proof of concept is a winner.

Into this second board I cut the same matrix of slots.  By then flipping this board over, each of the passageways is doubled in size (adding together the bottom and top halves), and also exposes a significant area of the soft, porous core of the MDF.  Each passage is now 10mm diameter, so that gives significant passageways for the air to pass through.

The vacuum was switched on again, and the top surface of this second board (the sacrificial board) was machined away with a surfacing bit (otherwise called a spoilboard bit).  And that is what this upper board actually is – a spoilboard.  When it gets too badly cut up, it can be flattened again, and this repeated until it is too thin, when it is then thrown away and a new board takes over.  By planing away 0.5mm of the upper surface of the spoilboard, the hard, compressed (and more non-porous) upper surface is removed.

Now I have seen a number of vacuum tables, and spoilboards with a large matrix of holes drilled though it.  Don’t need it.  The core of the MDF is so porous, that the vacuum can draw air directly through the MDF.  And that in a nutshell, is my vacuum table!

Upper board (spoilboard) from underneath, and the upper surface of the lower portion of the vacuum table

Upper board (spoilboard) from underneath, and the upper surface of the lower portion of the vacuum table

vac-4

Detail of vacuum table

Vacuum connection

Vacuum connection

I’m using a basic Shopvac for this, so I do have a bit of a concern that this will shorten the life of the vac.  I possibly need a vacuum pump, but this will do in the meantime.  The cyclone separator is to try to keep as much MDF away from the vacuum, to try to stop it being killed even more prematurely.

The proof is in the trial.

With a sheet of 3mm MDF laid on top, the vacuum switched on, and voila – it sucked big time, right through the MDF.  The board to be cut was held firmly, enough to run a trial nesting job.

Without tabs.

It was a complete success.  Other than the noise of the vacuum cleaner, I could not fault the process.  The vacuum will soon find itself in the shed next to the workshop, and switched on and off with the remote power switch I happen to have in there (the actual switch is right near the CNC as it happens).

Test job, no tabs

Test job, no tabs

 

I cut out about 5 patterns in total, and each time it worked perfectly.

Next, I tried another idea.  If the only reason for the material between each piece is to support the piece as it is being cut, it is really necessary if the piece is supported by the vac?

So I ran a large job with a full sheet, no tabs, and only 2mm between each piece (or more precisely, between each path the CNC was trying to follow).  And 5mm from the edge.

The result?

vac-5

Yield

Pretty much nothing left, what is gone is the project, leaving this sad skeleton.

So there you have it – my poor mans successful attempt at making a vacuum table.

Episode 112 Sabretooth

Plans from MakeCNC

Swiss Cheese

Slowly perfecting my processes, in this case for what is called a profile cut, where the object’s outer border is defined and the CNC router cuts the shape out.

I’ve been using a 1/8″ upcut solid carbide router bit – the 46100 from Toolstoday.com for the job so far, but knowing that it is not the correct router bit for the job.  What I should be using is something like the 46184 1/8″ solid carbide compression bit, or the 46180. (46237 and 46227 are also interesting bits, being 1/16″ diameter, which would be needed if doing nested work in 3mm MDF.)

Few reasons.

1. An upcut bit produces a lot of tearout in MDF.  While I can easily fix this with a quick sand of the top surface before removing the sheet, it would be preferable to avoid that step.

2. The upcut bit, especially at speed and with a large depth of cut, tries to lift the material being cut.  MDF is not a stiff structure, especially in a nesting situation which really turns the board to Swiss cheese.  It becomes almost impossible to stop the board being lifted, so I had to increase the number of passes from 2 to 5, and even then had a few lifting problems.

Not a fault of the router bit, I’m just using it as I don’t have another one of that diameter (or smaller) to work with 6mm thick boards in a nested layout, especially where I need grooves cut in the workpiece that are 5.9mm wide so they can slot together.

I’m cutting at 80mm/sec, and with about a 2mm depth of cut (DOC).  I know the CNC machine and the router bit can easily handle a lot more DOC, but my holddowns cannot keep up.  If I had a vacuum table, or even used a fair amount of double sided tape, that would be much less of an issue.

To stop the individual pieces being cut loose and walking into the cutter, wrecking them, I added tabs to each piece generally 2-3 per piece, 4mm wide and 1mm deep.  These are easily cut and sanded away at the end of the job.

It is important to ensure the cut goes all the way through in that final pass.  I have been using 0.5mm, but am thinking 1mm would work better.  Certainly, that means the router bit is cutting all the way through and partially out the other side, but that is why the tabletop has a sacrificial layer added.

What I made this time is the tropical fish (Angel Fish)……..

CNC-1 CNC-2 CNC-3and a stegosaurus!

CNC-4 CNC-5

It is very addictive!

And just for a sense of scale, here are both projects photographed alongside a bottle of wine (not so easy to see sorry!)

CNC-6

Now I just have 148 designs to go!

Plans from MakeCNC

Some first impressions

Very early on in the piece, but some initial thoughts.

The CNC Router is bloody heavy – not sure if it is 200kg, but it is a substantial machine, and for this sort of tool, the heavier the better!  There is no flex, nor uncertainty in the movements.

I’m having a little difficulty with the interface side of things, but that is a Windows machine issue.  Wish these things had Mac software to drive them!  Once I have gotten the computer up and running, switched on the CNC, then plugged it into the USB, it seems to run smoothly.

The controller is particularly heavy duty, and although the control box is large, it has plenty of empty space inside.  Not a bad thing for heat dissipation.

Love the fact that the software starts and stops the spindle – that is a nice feature.

There are still some fundamental things I don’t know about the machine yet – spindle speed range for one, achievable resolution for another.  Standard maintenance practices for the machine for a third.

The machine is designed and built by Keith, from YAS Engineering, who is also the inventor behind the Torque Workcentre. Quite the mechanical genius for these sorts of things!  This is one of the smallest CNC routers Keith has made, most are made to order, and some are monsters.  This model however is being made as one you can purchase off-the-shelf as a standardised design.  I just have serial number 0001!

Again it is very early days, but the comparison thus far between the CNC Shark Pro and the YAS Engineering CNC (don’t know what it will be officially called as yet) puts the YAS machine in a completely different league.  Yes, overall it is about $3000 more, but that extra 25% price (price of the CNC Shark Pro Plus) is more than justified by the significant build quality difference, including the quality (and quietness) of the spindle.  I’d say the 250% difference between the two, but that is subjective only!  The previous job was run at 11pm at night.  The entire neighbourhood would have been banging down my door if it was the Shark running the job – that Bosch router is an absolute screamer (and is only 1/4″).  I was also running the machine at about double the feed rate of what the Shark was performing at, and I was limited by the strength of the router bit, not the maximum potential speed of the YAS CNC.

Just jotting down some thoughts as I continue to get to understand the new machine.

Fast Learner

Here are a couple thousand words depicting progress…..

IMG_2733

IMG_2736

‘Nuff said!

Toolstoday.com 46100 1/8″ router bit
80″/min feed rate
20k RPM selected (but not sure if that is achieved on the CNC – have to find out what speed range it is capable of!)

Learning Curves

Short and steep!

Despite having some (limited) experience with CNC routers, I hadn’t tried parts fabrication before – cutting out one of the patterns as listed in my previous post.

The website provides next to no instruction on how to use the patterns, so I was left either watching the 98 or so minute ‘tutorial’ video that someone had made, which although useful for info, was very difficult to watch through, so I skipped about a bit to try to glean some answers.

Suck and See.

Biting the bullet is sometimes a faster learning curve, so long as nothing gets damaged in the process!

I created a path for one of the simpler dinosaurs – using a 1/4″ upcut solid carbide router bit from Toolstoday.com, created a few tabs so parts would remain in place once cut out, and sent it over to the CNC computer.

Some things to note.  When the program says something about it being outside of the soft limits, what it really means is that somewhere around the circumference of the design, you are going to ask the router to move further than it can physically achieve.  While that makes sense in hindsight, you can find yourself trying to work out why the program just wont run, quite fruitlessly.  Note to self – don’t deactivate the soft limits!

Somehow, even though I had set what the full depth of the job was meant to be, it only did one pass, rather than the two or three that would be needed to cut all the way through.  Have to look at what I missed there!  That is why we test these things to see how they work!

Where it did cut all the way through (I reset the Z height so it would achieve a full depth, and ran the program again – effectively manually causing it to cut through in two steps), the tabs I had made were no-where near large enough, and parts were coming loose and impacting the cutter.  Using an upcut bit exasperated the issue, as it was trying to lift the pieces out as well.

Four clamps on the board, one in each corner is not enough, especially as the board becomes riddled with cuts.  A vacuum table will be a significant improvement, when I get around to making one.

And a 1/4″ bit is too large a diameter for a 6mm thick design – none of the slots needed to join pieces together were cut, so I need some smaller diameter router bits for this sort of work.

Well, nothing was damaged in the process, and plenty of information was gathered to make the next attempt more successful.  No matter how sophisticated the equipment, there is always a learning curve on how to best utilise it.  Of course that is part of the fun!

SSYTC080 First Test Run

The first run of the CNC Router, using an existing code provided so I could test the setup.

The bench rocks quite a bit which is apparent in the video – this will be corrected by securing the bench to the shed itself.  Lots of momentum in such a heavy tool (and gantry).  The machine itself doesn’t suffer from it because of the size and quality of the stepper motors used.

Guard removed for visibility.  This is a quick test of the CNC, so the camera was set to record without particular attention being paid to the lighting, sound or quality, so don’t assume too much on that regard!

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