Sliding Mitre Saw Table Insert & 3d Printing Problems.

[philf]

A good friend gave me his old sliding mitre saw a few days ago.

All that was wrong with it was the plastic table insert was broken and he couldn't get a spare. His daughters had given him money for Christmas so he bought a new one.

I've had a 3d printer for some time and have made lots of whistles and Xmas tree decorations but thought that I'd have a go at something really useful.

Although not a newbie to 3d modelling I am a novice with Autodesk Fusion 360. I find it not very intuitive and some things which are very straightforward in some other 3d packages are seemingly impossible in Fusion - so you have to find workarounds.

After some time measuring and a few hours learning how to do things on Fusion I came up with this model.



At 384 mm long the part was far too big for my printer's 200 x 200 capability. Fortunately Fusion lets you split a model into parts so I split the model into 4 parts.



Conveniently, Fusion lets you export an STL file for each part.

I sliced the models with Cura 2.7 and used 100% fill with a 1mm wall and base.

Here's a pic of the original part with all the printed parts.



The parts looked basically OK (they haven't been fully cleaned up in the photos) but I was very disappointed with the holes. Considering I went for 100% fill and a 1mm wall they look decidedly ropey!





Is there a setting in Cura to improve this? There's certainly not a 1mm wall.

On assembling the insert I found the distance between the mounting holes was a few mm out - fortunately it was too long so I could cut 2mm of the ends of the centre sections and slot the holes. If I print any more I'll either compensate for the difference or leave the holes out at one end and drill/csk them to suit.

When I cut the ends off on the mill I was pleased to see that my 100% fill really was 100% and there was no evidence whatsoever of any voids.

Here's the insert in place. It isn't perfect but serviceable.



I did a test cut on a piece of scrap timber and the saw gives an incredibly clean cut. My friend even gave me 2 spare blades - one brand new!

Now I need a stand for it - I don't think that will be a job for the 3d printer!

Phil.

[Joules]

Phil, where a hole is critical or you need a threaded insert, I add small top hat bushes.   They are trapped under the part, the larger bush outer diameter spreads the load over more of the print where you can fit them in.  That is quite a common problem with the bore shell coming out and leaving you with a loose fit or ragged hole.

However, nice work on breaking the part up, my preference these days is to weld the parts and scrape them flush.   Welding can be done tig style with a soldering iron, use some filament as tig rod and chamfer the joints for welding.   Very large parts can be fabricated and best use of print grain used.

Try to find the option in Cura for overlap in printing and shell/skin.  I run 25% overlap to guarantee proper weld of the shell.  However I don’t use Cura, so not sure what they call this function.

[philf]

Thanks Joules,

I couldn't see overlap to start with but I discovered that in Options I could activate Overlap in the menu. There are hundreds of otherwise hidden parameters which I'll never try to understand.

I'll try a few test prints to see if it solves the problem. Failing that I could just do a pilot hole and drill and countersink afterwards. (Only an option using 100% infil density.)

I'd keep this as a screw together assembly as I can replace individual parts if and when they are damaged.

I can't visualize what you mean about adding top hat bushes!

Cheers.

Phil.

[philf]

Hi Joules,

I designed a test piece to try out the effects of printing parameters on holes.

Overlap (25%) made a huge difference and the top of the test piece looks very good. The first layer however wasn't perfect as the filament didn't appear to have stuck properly to the bed. (nozzle to bed distance was 0.1mm with a 0.2mm layer height).

I read up a bit about Cura settings and to get the first layer to stick better it recommends that you use a thicker first layer! This seemed exactly the opposite to what I would have expected and, sure enough, the print was poor. (Hovering over the parameters in Cura gives the same advice!) Someone else recommended using 90% of the layer thickness as a first layer - I've yet to try that.

I ran another print with small chamfers (0.25 & 0.5mm) added to the holes and the results (combined with the overlap) are excellent. Generally if you were machining in metal you'd countersink the edges of holes to remove burrs anyway.



The photo isn't that good - I just took it with my phone with the parts balanced on my laptop.

The top one is with overlap (25%).

The middle one was with 25% overlap and a bottom layer of 0.3.

The bottom one is with 0.2 bottom layer, 25% overlap and a small chamfer added to the holes - I'm happy with this outcome.

Cheers.

Phil.

[Joules]

Sadly using the overlap you loose some of the accuracy on components.   Holes can have a tolerance range as the overlap will cause a bulge in the adjacent filament that has been laid down.   One reason I print test holes, well thick walled rings to check I have the correct compensation in my models.  It can also vary filament to filament as they have different viscosity.  Printing with a chamfer at the start is the best way for first layer compensation.  The chamfer only needs be 3-5 layers deep, so quite subtle.

Don’t be afraid to close up that first layer gap, all it means is you end up with more squish.  If you hear the extruder clicking it means the gap is too tight.

[ddmckee54]

Phil:

Here's a couple of more things to think about:

I don't remember where I read it, but one of the recommendations that I found for the first layer thickness was to set that layer at 50%-75% of your nozzle diameter.  I print with a 0.4mm nozzle so I always set my first layer between 0.23mm to 0.3mm.

Be sure you periodically level your print bed and set your home position height of the print head.  I used to do this every time I started the printer from cold, but I'm confident enough in it now to only do this when I service the print head or when the first layer starts looking funky.

It's just a personal preference, but I always set the slicing software up to print the interior perimeter wall first when printing the perimeter.  The way I look at it, that way the interior wall should always be printing on a solid surface.  Even if you're printing an overhang on an interior corner, the exterior perimeter at least has a chance of bonding to the perimeter beside it.  If you print the exterior perimeter first, then it's hanging out there all by itself.  Maybe your printer will do it, but mine absolutely refuses to properly print a curve on free air.

Again, it's a personal preference, but I always print the exterior perimeter at about 60%-80% of the normal print speed.  I might just be imagining it, but I think I get a better surface quality when I do that.

On the first layer I try to set the extrusion multiplier to between 105%-110%.  I try to completely fill the first layer so that the nozzle is planning the surface flat.  I try not to extrude so much that the nozzle leaves ridges though.  I don't know if it's a fact or not, but I think that the ridges would just cause adhesion problems with the next layer.

There's a lot to learn at first, but just keep printing parts and doing what you're doing - trying to make the next part better.

Out of idle curiosity, how long did it take you to print the miter saw parts at 100% infill?

Don

[philf]

Thanks Don & Joules,

There's obviously an awful lot more to 3d printing than taking the printer out of the box and using it.

I'll do some more experimentation when I next need to print something.

Cheers

Phil

[philf]

Out of idle curiosity, how long did it take you to print the miter saw parts at 100% infill?

Don,

I wanted 100% infill because, looking at the broken part, you could see where the blade had taken some lumps out of the insert - with a non-solid infill this would have broken into the core and weakened the whole part.

I didn't time how long it took to print but Cura tells me that the end pieces were 2h 40m each & the centre sections 2h 34m (for the 2). A total of 8 hours!

The joy of the printer is that you can set it off and come back in a few hours to see the job done.

Phil.

[awemawson]

The joy of the printer is that you can set it off and come back in a few hours to see the job done.

Phil.
[/quote]

Or if you are unlucky you come back to a tangle of extruded media EVERYWHERE 

Though in fairness this has only happened once to me.

[philf]

Andrew,

Fortunately, I've not had a total failure yet!

I don't think I've mentioned my printer is a Balco from Aldi.

Phil.

[Joules]

Andrew, that is a nested part 

[ddmckee54]

The joy of the printer is that you can set it off and come back in a few hours to see the job done.

I think 3D printers in the shop are a lot like shapers. You can make just about anything on them except money.

Don

[Joules]

Phil, this is what I mean by a top hat bush, flanged bush.  They can be used as threaded inserts, or straight through for bolting down a print.   It takes the load so your print doesn't have too.  It stops the print creeping or cracking whilst spreading the load across more of the print.   This one is quite small and used in my mill dial gauge mount.

[philf]

Hi Joules,

That's what I'd call a top hat bush.

What I thought you were describing was actually something incorporated into the print and couldn't visualise how it could be done.

Cheers.

Phil.

[awemawson]

RS used to sell those with a knurled outer surface for pressing into a drilled hole to give a thread - not looked - they may well still do.

[philf]

RS used to sell those with a knurled outer surface for pressing into a drilled hole to give a thread - not looked - they may well still do.

Like these Andrew?



These are M4, M3, M2.5 & M2 internal thread.

Joules 'top hats' have a clearance hole through the middle.

Phil.

[awemawson]

Yes remarkably like those

[WeldingRod]

Those "heat set inserts" (according to McM) rock!

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