Designing a new router called Brevis-HD

[peteeng]

Hi All - I've decided on a Dia32x40L flexible rated at 2/4Nm $17USD for 3. This will be a good fuse and can be replaced easily if damaged. It maybe too big to get damaged anyway.... really should get a 25mm one and a 32mm and torque test both ways to establish mode and load of failure. Thanks Craig for the fuse idea this machine is going to have quite a bit of grunt for its price point. I still may bring the size of the motors down but smaller motors are not necessarily cheaper...Peter

[mactec54]

Hi All - I've decided on a Dia32x40L flexible rated at 2/4Nm $17USD for 3. This will be a good fuse and can be replaced easily if damaged. It maybe too big to get damaged anyway.... really should get a 25mm one and a 32mm and torque test both ways to establish mode and load of failure. Thanks Craig for the fuse idea this machine is going to have quite a bit of grunt for its price point. I still may bring the size of the motors down but smaller motors are not necessarily cheaper...Peter

If your Electronics are setup correct then they should fault when you have an overload condition, the drive train should be designed to handle any type of crash your machine may have Electronics should be in control not a cheap couplings that fail with normal use

[joeavaerage]

Hi,
the first time I crashed my machine, back when I first started I got a surprise how much force is involved.

Supposedly my stepper/planetary combination has a stall torque of 4Nm. I have since measured a short duration 'crash torque' of 19Nm. Through my 20mm 5mm pitch ballscrews
that results in a 'crash thrust' of 2300kgf!!! Recall this is a benchtop machine with low power 23 size steppers. It forced me to rethink the rather sloppy way I'd been treating
machine safety. Even a small machine can generate extremely high forces, easy enough to seriously injure. It was at that time a came to appreciate an un-intended
mechanical fuse.

Craig

[peteeng]

Hi Mactec - yes true. A machine has to have layers of safety built in. So current limiting and a mechanical fuse is a good idea.

Hi Craig - what diameter are your couplings? Peter

[peteeng]

Hi All - Some snapshots of the development model. I've started rebuilding parts to manufacturing level. The Development model has become cranky and falls apart occasionally so instead of fixing it I'll start again and tidy the part models and create proper sub assemblies. They have to have holes added and be checked for edge clearance etc. Then bolts and nuts to check they can be assembled. So into the drudgery part of the process. I think all the major decisions have been made so its pedal to the metal in CAD. I also have a meeting this week with the new sheet metal shop to check their tooling geometry. Last major decision is how thick to make the gantry. I planned on 3mm but seems its the weak link at the moment. The Z axis and saddle are very very stiff. So I have to decide what $$$ and stiffness to put into the gantry as they are the two big value parts of this project. I think they may drive the project $$ actually so may have to balance the structure around the gantry.

I have been running FEA models with and without shear stiffeners inside the gantry and they are needed when 3mm sheet is used. But over 4mm they are not needed as the corner stiffness is good. I have also been running push and pull loads and they are the same stiffness so no asymmetry there which is great. As usual the transverse stiffness is really high compared to the torsion case. The saddle is a bit complex but it works. Will review once the new model is built. By having the gantry bearings on top this has removed the issue of packaging the saddle bearings all in one place. Cheers and have a great week out there. Peter

[peteeng]

Hi All - Especially electronics gurus. I'm about to put a 500W 48V brushless spindle on Scoot my development router. Do I control the spindle by turning it on and off between the motor controller and the spindle? Between the motor controller and the power supply ? or do i turn the 230V on and off at the PS? Your opinions please. And the spindle has 3 wires so can I control it with a single pole relay? I think its single maybe a double, I'll look tomorrow...Thanks in advance... Peter

I think I can answer that now. Just looked at the BLDC motor driver and it has an enable pin so I expect I'll control that.

[joeavaerage]

Hi,
if its a brushless motor the three wires correspond to the three windings.

If the motor is spinning and under load suddenly opening the circuit between the motor and controller will result is a large voltage spike...best avoided.
The correct way to stop it is to command zero speed. Once it is at zero speed or close to it then open circuiting the motor at any of the three places
would work fine and no voltage spike.

Craig

[mactec54]

Hi All - Especially electronics gurus. I'm about to put a 500W 48V brushless spindle on Scoot my development router. Do I control the spindle by turning it on and off between the motor controller and the spindle? Between the motor controller and the power supply ? or do i turn the 230V on and off at the PS? Your opinions please. And the spindle has 3 wires so can I control it with a single pole relay? I think its single maybe a double, I'll look tomorrow...Thanks in advance... Peter

I think I can answer that now. Just looked at the BLDC motor driver and it has an enable pin so I expect I'll control that.

The Motor Drive is always the best place to look as most Drives have a way to Stop / Start and control the RPM

[peteeng]

Hi All in CNC land - This morning I bench tested the 500W spindle and the enable works fine. Soft start and finish and the quoted 12000rpm was spot on at 48V. Tomorrow I'll get it wired into Scoot. Waiting for an ER16 collet set. It came with a 10mm collet. So this week will be the last week I use the Makita. Its got nearly 700hrs on it not sure what the life expectancy is buts its had a hard life on Scoot. Cheers Peter

[machinedude]

nothing wrong with a simple plunge router or trim router to start out with. not every one is able to hit the ground running with top end ATC spindle or has the need for one right away.

[peteeng]

Hi Boys and Girls - Been busy doing drawings and adjusting holes for the new press settings. The 3mm sheet needs to have 6mm clearance to the bend line and the 6mm sheet needs to have 9mm but a little closer has worked before. On east coast of Oz we have been in drought for maybe a year plus hundreds of major fires everywhere. We've had record high temperatures as well. Well a big cyclone came close over the last 2 weeks and it has drenched the east coast with Mega tonnes of water. Nearby us has flooded and we've had to cross water to get to town.

The bridge in the photo is 200m from us and the night of the photo it went 4m underwater. Famine, fire and flood maybe pestilence next!! Peter

[machinedude]

i have to give you credit that binder with the master assembly drawing is about as professional as it gets hopefully it is water proof and floats by the looks of the weather in your neck of the woods.

[philba]

Good luck to you, and hope you stay dry.

[peteeng]

Hi MD - Thks for the credit. There is one step up from the binder. When I complete a machine for a commercial client I get the dwg set (build book) bound into a book, that always looks and feels Uberpro. Peter

[machinedude]

Hi MD - Thks for the credit. There is one step up from the binder. When I complete a machine for a commercial client I get the dwg set (build book) bound into a book, that always looks and feels Uberpro. Peter

it's a little bit different when your doing something for a commercial customer. it's more like a presentation and needed so you look professional to get the customer. i don't get into that end of the business. i'm just one of the guys that the prints get handed off too on the floor when it comes time to start getting the parts made.i thought the color coded tabs were Uberpro but a bound book i would think would take you as far as presentation can get you. then it's all about the design from there.

[joeavaerage]

Hi,
my only problem with plans, circuit diagrams and that sort of stuff is that I never have any UNTIL I've finished making whatever it is.....and then who needs plans???...I've
already made it!!

Craig

[peteeng]

Hi All - Brevis-HD has risen to the top of the pile again. The current task is to build a production grade model. This takes into account bending radii, hole clearances and any new stuff that has come up in the development process. So the development model is frozen and a new machine is built from its parts. But the new parts are changed from the dev parts if that makes sense. The client has selected the 1.5kW spindle and a 48V 500W spindle as the starting tools. I also have broken down the machine into assemblies. So as I rebuild I hold strict to those assemblies. As usual nuts and bolts are a major issue and for this build I have decided to include them in the main assemblies as a separate assembly. In this way they come out as a list in the BOM (theoretically). We shall see on that one....

The Z axis is the first to detail. I have changed the round rails to square rails. The round rails are mounted on a flange which is quite wide. By the time I add the hole clearance to prevent flaring the tool plate got quite wide. So the square rail using central holes minimised the plate width. Having to cope with various spindles turned the tool plate into swiss cheese at its bottom so I have used an adaptor plate for each spindle. In this way there are only the holes required and the adaptor plate can be removed and modified without pulling down the Z axis to add or change something. Looks pretty clean, I'm now onto the saddle assembly. Peter

[mactec54]

Hi All - Brevis-HD has risen to the top of the pile again. The current task is to build a production grade model. This takes into account bending radii, hole clearances and any new stuff that has come up in the development process. So the development model is frozen and a new machine is built from its parts. But the new parts are changed from the dev parts if that makes sense. The client has selected the 1.5kW spindle and a 48V 500W spindle as the starting tools. I also have broken down the machine into assemblies. So as I rebuild I hold strict to those assemblies. As usual nuts and bolts are a major issue and for this build I have decided to include them in the main assemblies as a separate assembly. In this way they come out as a list in the BOM (theoretically). We shall see on that one....

The Z axis is the first to detail. I have changed the round rails to square rails. The round rails are mounted on a flange which is quite wide. By the time I add the hole clearance to prevent flaring the tool plate got quite wide. So the square rail using central holes minimised the plate width. Having to cope with various spindles turned the tool plate into swiss cheese at its bottom so I have used an adaptor plate for each spindle. In this way there are only the holes required and the adaptor plate can be removed and modified without pulling down the Z axis to add or change something. Looks pretty clean, I'm now onto the saddle assembly. Peter

You can't be serious or have not put much thought into your Z axis, I think you need to rethink what you have just presented you don't want the motor and ballscrew moving up and down with the spindle

[peteeng]

Hi Mactec - Why? Works fine on my other machine and its needed for long Z movements. Peter

[joeavaerage]

Hi,
yes I'm curious as to why not as well.

In a bed mill the ballscrew and servo are mounted underneath the X axis and the ball nut is mounted on the saddle. The ballscrew and servo must therefore
move with the X axis....and it works. So why not a Z axis?

Craig