[davida1234]

top speed of 13m/min but it maybe better than that.

Nevermind, it is 512 ipm

[peteeng]

Hi All - Well we've finally arrived at Maximus's general arrangement! Now let it simmer for a little while so the dust settles a bit and then start rebuilding to a manufacturing level. The current model has a few quirks and its not subdivided into its correct subassemblies. Need to add bolts, threads, bolt holes and check that all things can be made. Then do the final FE work to distill it to 100% proof. Will write up a general spec sheet for information. Cheers Peter

[ericks]

Looking good

[peteeng]

Thanks Peter coin - You finally connected. Peter

[peteeng]

Hi All - I've had some very positive feedback in some PM's thanks out there for the feedback. Technically we are about to start Round 3 which is fine detailing. I've got to give it a break to catch up on some commercial work then I can get serious for the finish line. Also at this point it's good to let the project rest a bit so when I get back to it my head has some distance from it. Will check in on the thread and answer stuff but probably a week before serious design clouds start rising again. Peter

[peteeng]

Hi All- I've been asked about FE modelling the linear bearings. So I thought I'd discuss this a little. Modelling assemblies in FE can be quite tricky. Especially bolted or sliding connections. If the FE system your using cannot model these explicitly then you need to use approximations. In the case of the linear bearing if you look up their technical guide they may publish the bearings stiffness. I got these values from the bamburg thesis. The car is then subdivided into 3 parts, 1) The bolting volume 2) The contact volume and 3) the plastic ends. I model the ends so I can check clearances with parts etc. The bolting volume is set to steel and the contact zone is set to a nominal modulus. A simple model of a rail and car is made so you can place vertical and sideways loads on the car. You them adjust the contact zone modulus until the car behaves with the correct stiffness. In my case it worked out that the contact stiffness was near aluminiums and it gave a car vertical stiffness of 600N/um. I did not tune the horizontal stiffness as the modelling was in early stages but in Round 3 I shall do this as we want as accurate a prediction of deflection as possible. If you are using software that can solve contacts then you are probably capable of more complex modelling like bolted joints. Welds are straightforward as we consider them 100% efficient. Welds are difficult to interpret for stress results but for deflections in machine design we usually just connect the parts together as if the weld was not there. Similarly with a bolted joint just connect them using the entire contact surface. If I want to be a little bit conservative I often model bolted connections with washers between each bolted faying surface. In this way the area of contact is approximately correct. The software I use at present Simsolid evaluates bolted connections explicitly so I just need to model the connection to a manufacturing level no approximations needed. In conventional FEA you can model bolts in a simple to complex way. There are about 5 ways to do it in these levels. Too much to talk about here. happy to answer FEA Q's here or set up a thread.

In terms of machine stiffness using simple FE systems you are looking for order of magnitude issues. Typically to achieve say <1mm deflection at a design load you should be aiming at achieving <0.1mm in the model or better. Reality sucks so every post has to be a winner. The only reason to not aim high is if that solution is too heavy too big or some other compelling reason. The point to FE is its a tool to give you answers so play with it try things you would not be able to do in practice and see what happens. One trap with simple FE is you can design a paper thin structure and it won't buckle yet in reality it will crumple in a heap. So run linear buckling solutions if you have them and learn about buckling. ... Peter

Some time ago I came across the attached article on stepper motors. Its author is not noted so I can't acknowledge them. If someone recognises it please tell me who the author is.

[peteeng]

Hi All - Been checking some flange lengths and one is a no go, its too short. So figuring out a solution with the bender guys. Maybe a 45deg vs a 90deg will do it. Waiting for a comment. All the other bends are in air so I can make them minimum lengths. So I think it will work out. Fingers crossed. If I go back to 6mm for the part I loose a heap of inertia and its important. The 45deg bend is only 8% less stiff then the 90deg bend so I'll have to live with that. I could make it asymmetric to make up the diff... as one side is in air. Peter

[peteeng]

Hi All - Had a look at the working envelope and realised I can't get the spindle over the apron!! Usually this is easy as "normal" machines have a big overhang. So I'll have to extend the rail a little at the front so the apron is useful. Started adjusting flanges to benders specs, only mucked up the 8mm plate bends all the rest are good to go. Also started looking at the belt anchorage area and changed this a bit due to the bending radius flow on effects. Had to make these a Zed vs a U so will take advantage of this. Negative is that the motor mounts have to be a bit higher so will make them a bit thicker. Also started on its brochure... With the car beam up fold I'll try to integrate the bends so it can be bolted in two directions. This will give it better side to side support.

Talked to the metal benders today about thick coated steel for Maximus-L. But zincalum only comes in 2mm max and I think Max-L will be mainly 3mm or 4mm so looks like Max-L will be stainless steel as well. Peter

[Sterob]

I can't get the high powered N23 in 5:1 unless I buy 10 units so the 10:1 it is for now.

Hi Peter, Have you asked the question to the supplier? Maybe they will relent and sell you a smaller quantity. Worth an email, me thinks.....
Steve

[Sterob]

Need to figure out how to deal with the backdrive before it happens.

Not worth waiting to see if there is a problem before you fix it?
You may be making it more complex than you need to?
Find a fix IF you have Backdrive.
.....dunno.....just thinking out loud....

[peteeng]

Hi Steve - Yes I did. The 5:1 hi torque is not in their normal line but they can supply if I order 10 (a very small number for them). I have made special orders for anti backlash nuts from them before. I could buy the gearbox separate, still looking at that (but so far its cheaper to buy the combo not separate) but the 10:1 gives more power which is needed I think vs more speed.

Backdrive:::: From the numbers I think it will backdrive (not much friction in a ball screw) so need a solution before it happens. By the time I get brackets made ($20AUD plus), find a gas strut ($23AUD) etc I think it will be same cost as the brake and the brake is easy, small and clean. Other solutions springs, struts etc have variable force as well and this force is applied all the time, especially with a long Z axis travel, so a brake is great I think.

Plus with freight costs if I order the motor but not the brake, then I need the brake the freight cost will double the brake unit cost. So may as well go with it for the first order then find out. The brake is only $59AUD when bought on the motor $68AUD separate. Peter

I did not expect Brevis to backdrive using a plastic nut and a small lead but someone came into look at it and said can I put this engraver on it and I said lets find out. Was not much heavier then my ozito engraver and POP down it came so have to be certain with these things.

On another note I started my main computer this morning and it stopped. I tried again and it stopped. I turned off the power gave it a rest and turned it on it came up said HI then bluescreened and shut down. BUGGER!! So off to the tech waiting for the prognosis. Hope its not too bad, hate setting up all my programs again takes a couple of days to sort the licenses and keys and passwords etc. Never goes smoothly. Doing a lot of analysis and CAD I used to wear out hard drives in a year. Now with solid state they are not supposed to wear out but I do run the video cards hard so we shall see what it is. The computers 4 years old. Last week I said its over time for a new one!!

[peteeng]

Hi Gerry - I've been looking for the legend for all the colours and arrows and things for the threads. Where is the legend or what does it all mean? and how does it happen? Peter

[ger21]

Hi Gerry - I've been looking for the legend for all the colours and arrows and things for the threads. Where is the legend or what does it all mean? and how does it happen? Peter

If this is directed at me, I have no idea what you're talking about.

but the 10:1 gives more power which is needed I think vs more speed.

You have to be careful when using gear reduction with steppers.
A stepper's torque falls of rapidly as rpm increases. It's very possible that when the motor is spinning 10x faster, it may only have 1/4 the torque (or less). So when increasing the reduction ratio, at some point, you'll start seeing less power.

[peteeng]

Hi Gerry - Yes I appreciate that. That's why I use the mid speed numbers vs the top speed numbers. Legend - Finally something on this forum you don't know something about see the image attached. Peter.

[ger21]

The green arrow means you posted in the thread. Hover the mouse over it.
Red may mean there are new or unread posts. Not sure exactly.

[peteeng]

Hi All - Picked up my computer and its fixed. The video card had fried so that was an easy fix. So now I can back to some work. Peter

[peteeng]

Hi All - Getting close to Round 3 which I shall define as Manufacturing Detailing. An important milestone in a design is when you start doing drawings. I usually hang out until I feel that all the parts are well formed and accounted for. But we are about there. Change management and detailing are easier with drawings then models. So I think we are close. Plus I shall rebuild the model into its correct sub assemblies along the way so this will be the P3 model. In my first couple of machines I struggled to design a nice belt anchor/clamp. On Brevis this came together and it looks clean, works well and is fairly easy to adjust. On Maximus I've added another level of adjustment so it's easier to clamp and set the belt height with different bolts. It's fiddly to clamp and adjust height with the same bolt. Cheers Peter

edit - getting a bit art nouveau

[peteeng]

Hi All - Built new motor models and installed, currently contemplating the 25mm vs 32mm belt issue. The 25mm belt pulley overhangs the shaft 3mm the 32mm belt overhangs 10mm which is a bit far I think so for now I have it modelled as the 25mm belt. Need to built new motor mounts and return pulley mounts. I was going to make these one part reversible but I've decided to make them separate. I'd like to use cam followers for the return pulley axles but this will come down to cost plus they tend to have a large land on the shaft which would need washers to fill it up or use a custom spacer. Will speak to the bearing people tomorrow. Banggood and ebay have them but some reviews say they were a bit stiff. If I use two deep groove bearing I need to make a spacer for the middle more cost. Need a ~30mm wide bearing with a 12mm shaft Hmmmm.. Peter

[mactec54]

Hi All - Built new motor models and installed, currently contemplating the 25mm vs 32mm belt issue. The 25mm belt pulley overhangs the shaft 3mm the 32mm belt overhangs 10mm which is a bit far I think so for now I have it modelled as the 25mm belt. Need to built new motor mounts and return pulley mounts. I was going to make these one part reversible but I've decided to make them separate. I'd like to use cam followers for the return pulley axles but this will come down to cost plus they tend to have a large land on the shaft which would need washers to fill it up or use a custom spacer. Will speak to the bearing people tomorrow. Banggood and ebay have them but some reviews say they were a bit stiff. If I use two deep groove bearing I need to make a spacer for the middle more cost. Need a ~30mm wide bearing with a 12mm shaft Hmmmm.. Peter

This is about as close as you could get for a 12mm bore bearing https://www.vxb.com/LR5201NPP-Track-.../lr5201npp.htm

Track Rollers or cam followers you may find something close as well

Some automotive idler pulleys may work also

[peteeng]

Hi Mactec - I like VXB got my first V bearings from them. V bearings are a ridiculous price in OZ. Thats a good size I'll talk to the locals then to VXB. Ta Peter

I looked at the motor allowable moments and its 12Nm which for the 32mm wide belt would be a load of 46kgf and for the 25mm belt would be 66kgf. These are above what I'd expect for typical tool loads, but would prefer the 66kgf allowable. Plus they do not specify the SF, just described as "permissible". The 32mm pulley overhangs the shaft by 10mm the 25mm will be 3-4mm. So the 32mm is not off the table yet. Need to solve the return pulley bearing design this may tip the design direction... I use high strength loctite to bond the pulleys onto the shafts, don't use the key or a grub screw. Found the screws just vibrate loose and the key makes it hard to adjust when setting the pulley height, plus extra cost of getting the groove cut. Got to be quick with the adhesive. Peter