Accurate Strong Gantry

[vargai]

It was meant as more of an idea than a finished design.

It was not criticism just gathering data for a steel based light weight moving gantry DIY router that can be used in its scope and additionally I can check , try some solutions. I red about HSM spindle and HSM Al milling and aware of that this is also a wide spectrum so I will be happy with the result that a router can give.
Not forgetting the steel I am planning to attach an easy removable really small, geared spindle driven by the HS one with belt or directly coupled. (EDIT: i see now that the belt not good at this speed) In this method the supposed extension of the original spindle would be only about 60-80 mm and the force not bother the main spindle bearings
With 1:0,5 ratio (12000-to 6000 rpm) and quite enough torque I probably can make a typical steel milling with DIA 4-5 mm mill.
This would be making opening on a flat parts of electrical enclosures ( mainly doors) and mainly Dia 30,5 mm holes for push buttons.
The only problem is that the thickness is 2 mm but I suppose a 3kW spindle can do it with full DOC( the pre drilling- hydraulic method works but too slow and there are other shapes). This will not be bottleneck if I cannot do it just an idea.
pls adjust me if someone has experience.
One question about the steppers:
Normally they do their job and do not care of step loss and go on.
Is there any no too expensive mean, method to persuade them to stop at step loss and not multiply the mistake.
Thanks

[mitchejc]

I've run a stepper based machine for several years and when configured conservatively it will not loose steps under normal conditions. But if you are looking for something else maybe try EasyServo, its steppers that offer some of the features of servos but still easy to set up. Not sure about how the cost compares to the stepper motors you have in mind. They are basically steppers with build in encoders and run closed loop. They will try to correct lost steps and if they can't they would stop and give a fault signal it the error goes over a configurable amount of steps + some other cool features not really possible on other steppers without encoders. They also have a model for 110-220 volt AC so no power supplies required for those.

Nice video made by JazzCNC of how they work
https://www.youtube.com/watch?v=ZMZdCcLQc4M

Company that makes them
http://www.leadshine.com/category.aspx?type=products&category=easy-servo-products

I got them but my machine is in the build process so I have no idea how well they will work. I have played with them and its easy to get them running and the configuration software also allows many parameters to be modified if need be.

[vargai]

I got them but my machine is in the build process so I have no idea how well they will work. I have played with them and its easy to get them running and the configuration software also allows many parameters to be modified if need be.

Thanks, just thought there is some DIY made way but it is ok when it is reliable with careful set-up and parameters.
As you said the first to "play" and know the new built machine to find its sweet points.
In this thread and (others) you can find opinion of JAZZCNC of easyservo and he says it works excellent.
Little bit expensive but you have them and you can compare the price.
Could you tell this comparing the same torque stepper pls?

[Boyan Silyavski]

I am planning to attach an easy removable really small, geared spindle driven by the HS one with belt or directly coupled. (EDIT: i see now that the belt not good at this speed) In this method the supposed extension of the original spindle would be only about 60-80 mm and the force not bother the main spindle bearings
With 1:0,5 ratio (12000-to 6000 rpm) and quite enough torque I probably can make a typical steel milling with DIA 4-5 mm mill.

Belts are not a problem here. HTD belts are rated for these speeds. Problems are the bearings. Conical roller bearings will not spin so fast. Hence the 6000rpm limit on the spindles they sell. You will have to use angular contact bearings, not roller bearings, so they have to be over sized. Though i am still not sure if they don't use ball bearings on the spindles. You will have to check this and find suitable bearings and i don't see why it will not work. I have thought about that many times, despite what i said before. Plus my gantry on the machine i am building is rock solid. Though you have to have tremendously strong Z, cause 60-80 mm are big difference when we are talking about Z travel. On a router i mean.

One thing to note is that when we say -"this is bad, can not be done, not like that, you need other type of machine" , its not that it will not work. It will work.But not consistently, not for a long time. No perfect finish. Not be able to hold consistently precision. Ruining some element with time , /bearings/, etc. I can drive a city car where 4x4 car goes, but for how long? So actually its not a discouragement, its a reality check. I will be more than happy to see it done. Cause i will do it also.

Why don't you sketch your idea for the spindle and investigate the bearings.


As for the motors you could fit cheap encoder to steppers and then feed the signal to the breakout board/you will need available inputs/ . When out of programmed way, the machine could stop so you don't damage material. I have a plugin on my PC that does exactly that. Though that's not a true closed loop. The closed loop motors will push till all is where is meant to be and stop only if they could not overcome the force. If you decide to go this way, i will send you the plugin. There are cheap normal steppers with integrated encoders. though definetely will be mistake for the sake of encoders to buy some steppers witch are not low inductance.

Just use good PSU, good board and motors and you will not need these. Though closed loop would be nice on a metal working machine.

[Ross77]

What spindle are you planning to use? I know there were a few mentioned but cant see which one you decided on.

The thing to remember with spindle bearings is the amount of pre-load they have which affects the rigidity and speed.

Taper bearings with a heavy preload will be super rigid and cut hard materials but will be limited to a low speed. If your milling steel this is what you need.

Angular contact (AC) bearings are similar and the heavier the preload the more rigid they become. Due to the reduced contact area they have a higher speed capability but lower load bearing capacity than a similar sized taper bearing.

So as most of the high rpm (15-20k) router spindles will be using AC bearings then the rigidity will probably be low. This will be the weak link and no matter how strong the machine is it wont be at its best.

Bottom line is you can have a machine capable of both but realistically you will need two separate spindles.

You could always get high end spindle with hydraulic adjustable preload :0)

I have 75x40 precision AC bearings for mine and should get me up to 12k for HSM with adjustable preload and with oil mist lubrication lol.

[vargai]

What spindle are you planning to use?

2,2 or 3 kW water cooled chines spindle fit to a general router
The secondary small spindle would be a really light loaded ocassionally used one for the special purpose mentioned.
Short video is attached. The door steel sheet is 1,5 or 2 mm. At issue.That is why I do not want to pay too much attention to it but some searching is not a sin. I will show up some details in the answering to Syliavski and waiting for your comments.
By the way do you have something more then Chinese spindle do not you? from low rpm to 12000

[vargai]

Why don't you sketch your idea for the spindle and investigate the bearings.

Here is some sketch and I am almost sure the for DIY use with a short 5 mm flute cutter this spindle is quite strong enough.
Cutter is clamped by Weldon @6000 it works, lower AC bearings are coupled and after installation it will be preloded
grease lubricant also fine here.
Some safety issue should be considered:
The drive shaft in the ER20 collet should we carefully machined including the pulley to reduce the unbalance.
I would use double key opposite to each other.
Good cover must be done to protect the belt and user.I checked my 170 mm blade Makita plane , it run @15000rpm so you are of course right regarding the belt application. Here ribbed V belt is used so i think 15 mm wide HTD3 is sufficient here.
If you flip the pulley on the mini spindle to the top to skip the belt from the milling area you have to use some adapter plate .
This is not the first thing i make now but probably later Paris is well worth a mass.

[Boyan Silyavski]

Some technical info and bearing sizes and data . There are some force calculators there and so on. May be you know them already but let be here on one place.


Here is the 3kw/3.2-4kw i believe also/ spindle with all sizes if you dont have it at hand. I took them personally :-) .This is the original Guanzhou spindle with the 4 bearings and the black rings. Maybe enough place that the attachment could be clamped directly at the spindle there.

Hope that helps. When i have time will sit also and see if i have some ideas.








These are the bearings and dimensions of the BT35 spindles for reference:








Here is some belt info. If i read it correctly best would be HTD3- HTD5 belt or GT belt even better . Dont be put off by the lower life the figures show. After all one belt is 1-4 euro only. One thing to note is that wider than necessary is not a good idea.

[Ross77]

The general arrangement is really good. Back to back AC's and floating end bearing to allow for thermal growth. Are you making this or buying?

My only concern is that by driving it from the bottom you are increasing the distance from the cutter to the bearings and compromising the design. The belt tension will also pull the spindle off center. Can you drop the bearings down in side the pulley?

I'll try to find my old spindle designs and show you what I mean, I have gone over sized on the bearings so the taper of the collet is inside the bearing.

what size bearings are they? For 6000 rpm have you considered roller taper bearings?

This is of course me being super picky, your design will work but just offer suggestion to maybe improve :0)

[vargai]

The general arrangement is really good. Back to back AC's and floating end bearing to allow for thermal growth. Are you making this or buying?

My friend is renting a small shop and generally I got him to machine the part,and I will put them together.
There are a Bridgeport VMC, a Colchester CNC turn and a Hungarian CNC turn. I used to work here but recently after the daily office job I prefer to have a little brake. That is way I would like to have some machines at home where I can work any time that fits to me.
The bearing is 15 mm bore -for an entry level spindle is Ok but any design comes in handy, thanks.

PS: I have adjusted my setting so the vid is already visible at my previous post to you