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    Activation process peteeng's Avatar
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    Default Brevis a new CNC Platform kit

    Hi out there - This is my first thread. I thought I'd put forward a thread about a CNC platform I have just completed. It's called Brevis and it came about as I required a demonstration machine for the Brisbane Timber Show I intended to display at this year (2019). Unfortunately there was a muck up with the paint, twice! so I missed the commitment dates for booking space. So back to the beginning. Nearly two years ago I designed and built Scoot a half sheet router as a learner machine. I've suitably thrashed Scoot over the last 1.5 years and it's time to make a new big machine to replace Scoot. But its too big to lug around to shows so I decided to make a small one, hence Brevis. Brevis turned out really well so then I decide to sell it as a mechanical kit. The Maker could use it as a carver, router, 3D printer, food extruder, plotter, camera dolly etc etc.

    To begin with I use Alibre, Rhino3D and other software to design things. I'm a mechanical engineer and design large mining equipment, medical equipment like patient lifters and I'm involved in automotive and yacht structures so should make a good go at a router. I found good mechanical bits hard to come by, the electronics, electrics, motors and controllers etc are all off the shelf stuff. So Brevis started with a few rules. 1) It is a minimal function machine. In other commercial projects its common to analyse the structure, figure out what it should look like then make it bigger. In this case I wanted to stay with the minimum calculated stuff. 2) Minimise bolts and fasteners. Seems with many kits there are 100's of bolts to deal with so don't go that way 3) With Scoot I researched bearings ad nauseam, even made my own bearings and concluded that linear rails are the best solution. So I've stayed with 20mm linear rails for Brevis same as Scoots. 4) Simplify, simplify, simplify is the mantra... egt the motor mounts are used one way up, by turning them over you have a return pulley mount with tensioner, one part two jobs.

    So I start designing a parametric assembly in Alibre and start getting all the compromises lined up. Looking in my log I set up the files early July 2018 and I ordered parts and had it moving in Nov 2018. I decided to make Brevis from mild steel and have the parts powder coated so they looked good. Bad move. The coater I went to put on nearly 0.7mm of paint so the parts did not marry and many of the holes were closed over. Even though they had 0.5mm allowances on them. I had to drill out the holes oversize and file off the dags. I took it back and they repainted the ones with drips and excess paint but I was not a happy camper. I'm about to have B-1 painted by another painter (fingers crossed!!) So next time I'll do what I did with Scoot and have them made in Stainless Steel & Aluminium. No paint to change fits.

    I probably went through 12 or 16 design rounds to get to the current design. Simple is often not simple to get to. So the main features are brazed columns (to remove bolts and make stiffer), laser cut and bent steel parts. AT 10mm belt drives for X&Y, Z is an integrated drive screw stepper. I had to build three sets to get to minimum orders for processing and to make the unit costs reasonable so there is Brevis-1, Brevis-2 which are built and tuned and B-3 is a mechanical kit. B-1 uses 400 step per rev motors and a "in one box 4 axis controller" from stepperonline which was a joy to wire and use. B-2 I decided to use a 5 axis BoB so it could become a printer or extruder or rotary axis etc easily. I had a 1:5 geared stepper motor for another project so ordered more of these so B-2 has 1:5 on the X axis and a 1:10 on the Y axis. This makes it a very grunty and very fast machine. The extra torque accelerates quicker and 17m/min is quite easy to get to in <300mm.

    Being an engineer who has calculated the parts out and can calculate motor loads, torques, etc and do the structural analysis I also thought this thread should contain some of that stuff as well if there is interest. If someone whats some insight into how to calculate something ask and I'll write something. Like this. Blog | CarbonWorks – Engineering Excellence see gantry construction. Or this one; https://www.facebook.com/ScootCNC/vi...4646323343571/ eg why braze a column vs weld it? Well welding melts metal and when the metal solidifies it shrinks and distorts the part. This means I would have to remachine the part for flat fits, which means more cost. Brazing only heats the area to 650deg C and does not melt the part so there is minimal distortion. I braze aluminium and steel often and if done right these need no cold setting or post machining. Plus by laser cutting I can have tabs and slots made in the parts so they are self jigging.

    I use Mechsoft CAM software and UCCNC with a UC100 for motion control all of which I have found easy to learn and use. So now to see whats next. Also I have posted in the Ozzie forum as nothing much has been added to this in a while... Regards Peter

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    Member dharmic's Avatar
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    Default Re: Brevis a new CNC Platform kit

    Good to see any finished build, nice to see something happening in sleepy old Oz instead of the usual Chinese imports.

    You've certainly winnowed down the structure from the usual. I'll be honest, the gantry columns on single bearings looks like it would wobble all over the place. But every machine I've seen has come from the overkill design team, and the tool mount looks like this one is going to be doing pretty light duty (but fast). So maybe the numbers won't lie and it'll play nicely. Keep us posted!

    Be very interesting to see how it runs, if you can be bothered putting together any video of it going.



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    Activation process peteeng's Avatar
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    Default Re: Brevis a new CNC Platform kit

    Hi Darmic. When I designed the machine I did not intend it for routing work. It was intended for laser and plotting. But once built couldn't help putting on a small engraver. Now I'm making a mount for a 1/4" collet machine for it to see how that goes. People want routers/carvers it seems. Plus they want to cut aluminium which is a way different machine to a usual small router. I'm sure Brevis would run well as an engraver. Scoot ran with single bearings on all axes for quite some time so I know they work if you look after them. But if you do heavy wood work or plastic they do get tired fast. Brevis is designed so you can bolt on extra bearings for the gantry base and the gantry if needed without changing anything. If the Maker wants it as a router I set it up with heavy preloaded cars, that makes it much stiffer and lasts longer. Peter

    https://www.facebook.com/ScootCNC/vi...1610488285151/

    Scoot 3D routing https://www.facebook.com/ScootCNC/vi...4002371109380/



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    Member dharmic's Avatar
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    Default Re: Brevis a new CNC Platform kit

    Nice one!



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    Default Re: Brevis a new CNC Platform kit

    Hi Dharmic - Since I've been running Brevis Alpha and the enquiries I have are for routing I've decided to have these as options:
    1) The addition of a support beam to the gantry rail 50x50x1.6 stainless steel
    2) An improved Z axis mount with one bearing (stiffer) or
    4) An improved Z axis mount with two bearings (much stiffer) &
    3) The option of heavy preload bearings, I use light preload as standard.

    If as you say you build an overkill machine you never know where you can lose stuff. But in a minimum function machine you quickly identify issues or where you can add stuff. Peter



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    Default Re: Brevis a new CNC Platform kit

    Nice I found the more stable I needed my machine the bigger it became and so did the cost ,I still have a lot of fun and plenty if accessories to add enjoy.



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    Default Re: Brevis a new CNC Platform kit

    I do a lot of structural simulation. Here's links to a Brevis simulation. Its applying a 20kgf load transverse and longitudinal to the tool. Turns out the gantry rail twist is the biggest deflection.

    https://www.facebook.com/ScootCNC/vi...2502242763004/ transverse load realtive to rail
    https://www.facebook.com/ScootCNC/vi...7040780975671/ longitudinal load

    cheers Peter

    these are linked as I can't upload MP4 files to this forum. I tried zipping them but that failed. I'll try something else later.



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