[peteeng]

Hi OCD - I looked at the Print NC builds and there is certainly some impressive machining going on there with some of the builds. Scoot is bigger and stiffer then the Print NC so should do the same cuts. The ones with the ER20 spindles do well as the bearings are big and the they use a big bit. They are also using adaptive and HSM techniques that I am starting to look at now via Fusion360. When No2 gets running I shall try to replicate some of their cuts. Peter

[peteeng]

Evening all - Did anyone hear the scream? I've had an epoxy disaster. The two boards with inlay and fill didn't go off ?? I had them in our honey warmer (32C) for two days and they stayed gummy. I used my oldest epoxy as the black pigment covers the yellowing so I thought that 10 year old epoxy maybe off. But I did a non pigmented test and it hardened properly overnight. So the pigment inhibited the cure. The pigment is old. The universal pigment usually accelerates the cure, so it goes in the bin. I milled down the insert and when it got to the epoxy it started throwing black gummy balls everywhere. Had to clean the machine base with acetone. I was going to route out the bee insert and redo but with this experience they both get chopped up into small boards. So start again on that project!! Peter

[JayneV]

Oh bugger, that’s a shame, it was looking so good.

[peteeng]

Hi Jayne - there's always a next one... Peter

[OCD-Components]

Hi OCD & others - I'll explain a few things about "Aluminium". If you design a machine for cutting timber and plastics it can be lightweight, use cheap bearings and cheap spindles and it will be an economical, satisfactory machine and the Maker will be very happy with it for years of use.

As soon as you mention aluminium or aluminum the machine designer is in a quandary. The machine has to be much much stiffer, the spindle has to be good quality otherwise you kill the bearings, you have to consider lubrication eg if you have a timber baseboard it will get contaminated then when you go back to your nice clean timber jobs it will transfer and muck up your timber finishing. The "mill" will throw swarf all around your garage and it will take a long time to clean up. So an enclosure is needed. Then there is the question about accuracy of the cut, what expectations do you meet? Does the Maker expect a finish like off a mill? or will they put up with a bit of a scuff? Do they expect 0.01mm accuracy or 0.1mm? You read some specs for small machines at 0.001mm and that can't be right. If the machine is your own design and home built you will discover all of these things along the way and you will put up with it. If its your hobby then that's part of the adventure.

If you buy a commercial machine the supplier has to make an accurate presentation of what the machine can do. This is difficult to define. Chinese router machines often say they are engravers not mills for metals. Makers say they only want to cut Al "occasionally" well it doesn't matter if you cut once a year or every day the machine has to perform correctly. So now the designer has to use heavy bearings, make a machine at least 10x more stiffer (should be 100X stiffer) then one that cuts timber, use a good spindle and then how far do you go? From a <100kg machine you jump to a mill that weighs 2 tonnes. The consequences of that are much more costs and stuff is involved. So the machine is "expensive" and the Maker asks why?

Then there is the question of depth of cut DOC. A std DOC is one tool diameter. If you expect a light router to cut AL 6mm deep with a 6mm tool forget it. So light routers cut aluminium by using 0.5mm DOC maybe 1mm DOC and go around the part many times. This wears out the tool fast. Then the small machine can't feed fast enough so its scuffing around the part vs cutting. ie they cannot achieve the correct chip load. But if the Maker is doing this once a month for a personal part then that's fine. If the Maker is trying to make money from this part they won't.

So when aluminium is discussed I have to get a good understanding of what the Maker wants to do and usually I run a sample so they understand what the result is. Often they don't know what they want to do its just a thought bubble so they are making decisions purely on the $$$ value. Scoot-S2-02 in the workshop currently has a cheap 600W DC spindle. It "cuts" aluminium fine but it does have a big runout and it does have a weak shaft which I have bent and straightened twice. Its edge quality is poor by mill standards. You get what you pay for. I tend to build using the cheap alternatives to discover how far they can get you. No point in me building something with the best stuff as it won't let you down. Makers tend to go the cheaper route... except in spindles it seems. I suggest 800W AC and they always pick the 1.5kW seems bigger is better...

Its time to upgrade Brevis/YaG/Scoot-S2 to an AC spindle with good bearings to see how that goes, I have thrashed the poor DC one enough. Scoot-S3-01 in build has a 1.5kW ER17 spindle and I'm interested in how that goes with Al.

So OCD publish a photo of what you want to cut in Al and I can help further... Peter

Hey Peter...thanks for the reply. I can already cut alu with the machine I have, but there's always room for improvement, basically it's not rigid enough being extrusion based, it's my first CNC so have learnt alot over the last 2 years of use. It was really a test to see if I liked doing it, and I do so will move forward with it. At the moment just doing my homework for the next machine, my issue too is that I have very limited space in my shed, I should be able to squeeze 600 X 1200 cut area machine in there, so long as the structure itself is not too bulky, but there in lies my dilema, seems to get the rigidity, I need bulk/mass....anyway....in the meantime I keep researching, but so far Print NC is winning...cheers Mitch

[mactec54]

Hey Peter...thanks for the reply. I can already cut alu with the machine I have, but there's always room for improvement, basically it's not rigid enough being extrusion based, it's my first CNC so have learnt alot over the last 2 years of use. It was really a test to see if I liked doing it, and I do so will move forward with it. At the moment just doing my homework for the next machine, my issue too is that I have very limited space in my shed, I should be able to squeeze 600 X 1200 cut area machine in there, so long as the structure itself is not too bulky, but there in lies my dilema, seems to get the rigidity, I need bulk/mass....anyway....in the meantime I keep researching, but so far Print NC is winning...cheers Mitch

Depends on what you want out of a machine like this, the design of this machine is simple but poor in terms of rigidity, and is most likely no better than what you have, if you are cutting mostly Aluminum Brass then open Ballscrews design like this machine has, is a no. They build them like this because it is simple to build like this, there is also no accuracy to this build, having no machining of the main mounting surfaces is a big no, if you want a rigid and accurate machine, you can't mount a Linear Rail on a painted steel tube and call it good, look up the requirements for Linear Rail mounting and then you will get the picture of how bad this machine design is.

[OCD-Components]

Depends on what you want out of a machine like this, the design of this machine is simple but poor in terms of rigidity, and is most likely no better than what you have, if you are cutting mostly Aluminum Brass then open Ballscrews design like this machine has, is a no. They build them like this because it is simple to build like this, there is also no accuracy to this build, having no machining of the main mounting surfaces is a big no, if you want a rigid and accurate machine, you can't mount a Linear Rail on a painted steel tube and call it good, look up the requirements for Linear Rail mounting and then you will get the picture of how bad this machine design is.

What I want out of the next one is not to take a sideways step, and in the realm of DIY or even anything under 10-15K pre-built, doubt there will be any machining of the main parts (unless you have a mill, I don't). There doesn't seem to be any DIY design that stands out from the crowd, it's just more of the same, unless you want to get spendy, IMO.

[mactec54]

What I want out of the next one is not to take a sideways step, and in the realm of DIY or even anything under 10-15K pre-built, doubt there will be any machining of the main parts (unless you have a mill, I don't). There doesn't seem to be any DIY design that stands out from the crowd, it's just more of the same, unless you want to get spendy, IMO.

A machine the size you want would not cost very much to have the main mounting surfaces machined by someone, if that is too much, then you should not even consider building a machine
DIY builds mostly have the machining work done in a machine shop, if they can't do it themselves, there are many builds like this

[peteeng]

Hi OCD - So if your only doing panel work your accuracy requirement is not high. Print NC bolts square rail to standard cold formed RHS. This is potentially a pain point. There are many threads here where Makers do this and the cars immediately jam. So pick your RHS carefully. Plus the Print NC mounts the rails on opposing sides so you cannot level them in that direction. Even the paint thickness can be an issue. I'd look at heavy aluminium extrusions vs the steel, I'd expect them to be straighter then the steel sections. Make your Z as low as possible if you only doing sheet metal work. Once Z gets up you start to need lots of rigidity....Keep chasing the Grail like we all do

By the way rigidity/stiffness is not related to mass. My current best choice material is beryllium, less dense then aluminium at 1850kg/m3 but stiffer then steel at 287GPa.... Used lots on spacecraft...If your only doing light panel work consider a vertical or near vertical bed machine, saves a huge amount of floor space. Peter

[peteeng]

Morning all - Since were talking aluminium I did a small job on Scoot this morning. Prior machines had the support bearing above the adaptor plate but this time I decided to put the bearing at the bottom to maximise the Z. So I had to relieve the old adaptor plate. The feed is 1200mm/min at 12000rpm. The tool is 6mm 1F DOC 0.5mm. The spindle is a 600W DC with some runout. Its not bad on cuts but precesses on plunges. Edge quality is acceptable for the job, poor compared to a mill. This is a chip thickness of 0.1mm which maybe a bit thick some charts say CL=0.05mm for a 6mm tool... if I do finishing cuts at 0.05mm the bearing clearance allows the tool to be pushed away from the job.

The pocket provides spanner clearance if you have to get at the nuts in-situ. I don't want to burden the spindle too much with DOC. When this one dies I shall replace it with an 1500W ER16 AC spindle. By the way, BST have supplied the manual for the inverter so reading that with interest. I'll do some trials on Matts 1.5kW spindle before it leaves the workshop. I hope to fire the inverter up and check its parameters tomorrow. Peter

[peteeng]

Hi OCD - One way to look at your puzzle is; What are your typical cutting parameters now on a typical job? and what do you want to achieve? Usually you want to increase feed speed. So since Power=forcexvelocity you have to increase your drive system force by a factor of 2 (assuming you are at the top of this machines capacity and you want to cut at 2x current feed but if you want to cut at 5x current feed then things have to be bigger) then the torque has to double etc and the machine stiffness has to match these upgrades..... Peter

[peteeng]

Hi All - To finish off the epoxy thing. Here's a shot of the soft epoxy 5 days after its been mixed, still soft like mastic. The non pigment batch went hard as per usual... Peter

[joeavaerage]

Hi,
how much pigment did you put in? I've ever only put in a teaspoon worth or so in a 100-200ml epoxy mix. I wouldn't have thought that pigment would
have any effect on the hardening reaction.

Craig

[peteeng]

Hi Craig - Usually 1-2% by weight addition. This time I just picked some up on a stick and added it until it was "black" but the pigment is very old so I'll get some new stuff and test it before I use it next time. I've added all sorts of stuff to epoxy and its always gone off so a mystery. Won't play with the stuff or chase that rabbit hole just goes in the bin... I always weigh out the mix, my scales are good to 0.1g so mix ratio is good....Peter

[luke peter]

You have done a lot of composite work Peter, have you come across a filler effecting cure before?

[joeavaerage]

Hi,
I've done heaps of boat work and with epoxy its common practice to mix several times the volume of the epoxy with fillers, like colloidal silica, micro-balloons and for a glue,
micro-fibers, all without affecting the cure.

The only thing that is 'verboten' is to introduce any chemical, or even a solvent because it becomes non-reactive molecules within the resin matrix and always degrades
the cure properties.

For the small amount of pigment that Peter used I'm surprised that it could have affected the cure as much as it has. It would tend to suggest that one or more of the
components of the pigment has actively interfered with the epoxy reaction, but why would any pigment have components that could degrade the epoxy cure???

Bizarre.

Craig

[peteeng]

Hi Luke and Craig - Yes epoxy is usually bullet proof if you use the correct mix ratio. There are metal ions that can inhibit epoxies cure. Luke this is the first time in my memory that I have had an epoxy failure. The universal pigment eg pigment used to tint acrylic and solvent paint at your hardware has a few ingredients. I've done some reading over the last couple of days with no joy to an understanding. The "vehicle" is usually a glycerin and at low addition rates this just floats around in the solid epoxy like any other solid or liquid addition. There are components to prevent agglomeration, improve wetting/dispersion and improve compatibility with water and solvent systems. So its chemistry is complex. The black I have is quite old maybe 2 years plus which it is not intended to be around that long. Its clever chemistry in that one additive used, one end likes the pigment and one end likes the water but the opposite end likes the solvent so it switches ends depending on which paint it gets chucked into. I've added high loadings of silicon oil, teflon oil and various other things to epoxy with no curing issue... But I may do a test and see if it does it again with measured amounts. But I have many things to do and curiosity kills the cat. The epoxy is over 10 years old, the hardener is yellowed but it still works... fine for filling wood probably not good to hold a plane wing on with...

The main error that stops epoxy from curing is incorrect mixing ratios. Epoxy does not use a catalytic curing mechanism it cross links two constituents (stochiometric - thanks spell checker). These have to be in the correct ratio so the linkages across these agree. You can't make it cure faster or slower by adjusting the ratio you just screw up the chemistry. Then there is temperature. Epoxy needs energy to start curing and if the temp is down this reaction cannot occur. If the epoxy is "thick" once its going the exothermic reaction will take it to near completion. If the hardener is low activity ie a casting resin or a resin intended for thick sections and you use it in thin sections like laminating or coating then its surface/volume ratio will give off enough heat to keep it cold and again it won't cure. Need to add extra heat in that case to kick it off but should use the correct epoxy/hardener for the job. Retarders are usually aromatic diluents that keep the R/H apart longer until it evaporates, then the reaction can occur. Got to have a failure occasionally to keep one on ones toes....

Moses supposes his toeses are roses they say....Peter

[peteeng]

Hi all -some info on spindle power requirements - Peter

A New Milling 101: Milling Forces and Formulas | Modern Machine Shop (mmsonline.com)

[peteeng]

Hi All - I'm designing a skate board mould that I will cut on Scoot. Its the first project in Fusion from part to tool path. Been a mission to learn but starting to get the hang of fusions language. I sliced this one up a bit so I could see the form better... I ran the CAD bandsaw though it a few times... Peter

[peteeng]

Evening All - You Fusion CAM gurus - can a stock geometry be brought into fusion? Since I'm laminating a few chunks of wood together for this job it will be a strange shape. So I want to optimise cutting time based on that shape not a block. Any ideas? Otherwise the tool will have a lot of air time at the moment. Peter