[suspension]

Hi joeavaerage/Pete/ardenum2

Thanks again for calculations. I think with this help I can settle with 750W servos minimum and if price does not matter much (which is the case for JMC) go with 1KW.

Regarding your calculation, you convert linear mass movement to a rotational momentum. During this conversion, only kinetic energy is considered. What happens to the thrust required to overcome friction of 4 linear bearings?

In many occasions you mentioned stiffness. And stiffness is better with 32mm screws than 25mm. Given that 25mm gives you enough life span, what additional benefit can we expect from 32mm with its higher stiffness. I am just trying to understand than arguing!

Apparently, LTM is manufactured by this company: Deans Manufacturing Group. They sold their first ballscrew business in 1988 and the brand was re-named as HIWIN!
Anyways, I could not find much reviews, information on this brand and got some second thoughts. These cant be as good as NSK/THK/HIWIN in my view and if I wait/search enough I should be able to find what I want from these known brands instead.


I will consider your comments regarding braking and counter weights after finalizing ballscrews. As mentioned previously by others, the design of my machine is going to be based on the screws I can find.

I also want to get your thought on this build:

https://www.youtube.com/watch?v=-OVbqG7wIHY

He explains nicely how he does various things such as aligning rails etc. One very interesting thing I saw in his build is he uses linear encoders for all Axes. With this, you do not derive linear position by rotational position so any in-accuracies caused by changes in lead of ballscrews are avoided. Also theoretically backslash should not be an issue as well. This way one should be able to use C7 ballscrews. After ardenum2 mentioned my selected C3 ballscrews looking like rolled, I read a bit about this and found an article/research paper which mentioned thee points. Any one of you have any ideas on this?

[NordicCnc]

for cold casting inserts you'd use a steel piece that's been stress relieved, you'd have to ask the shop about it. I don't think they stress relief extrusions which is probably why it deformed after machining.

If you have it machined at a company the result depends on the machine they used. I've seen many builds where even after machining the result was poor and not to spec as ordered, in the end the person had to use steel epoxy. To ensure proper surfaces you'd probably need to pay for grinding too.

Think it's better to just get the DWH instead of trying to reinvent it, it's not that expensive anyway. It's a ready made product and it's been proved and tested, you're unlikely to match it's performance if you try to make it yourself.

Unpleasant surprise. Shipping DWH outside out Germany is very expensive. I asked for a quotation to ship to Finland and it wad 340€ just for the shipping, because it is "dangerous goods".. Then I found SKC, a similar product but they only sell to businesses, and they also said freigth costs are, quote "Very High".. So DWH is out of question and so is SKC, unless I really can't find any substitute. Dang.. feels bad to purchase a 50€ product and pay 340€ for shipping.

Weicon A seems to be something which could be used instead for precision casting. I saw CHIPLOAD on youtube use it in his lathe build.

Thoughts, any other alternatives for precision casting rail surfaces?

Skickat från min SM-A528B via Tapatalk

[suspension]

Hi,
one last piece of the puzzle is the mass of the Z axis.

My Z axis, including the saddle, beam and spindle is probably about 50kg max. I determined that I did not NEED any mass balance or air cylinder.

My reasoning goes something like this:

Lets apply 1Nm to a 32mm diameter 5mm pitch screw and calculate the thrust it generates:

1Nm = 1N @1000mm is equivalent to 62.5N @ 16mm (the radius of the screw)
The mechanical advantage of a 5mm pitch screw on a 32mm diameter circle is:
(32mm x pi)/5=20.1

So for 1Nm applied to the screw we get 62.5 x 20.1=1256N thrust or 125kg force!!

Thus to support my estimated 50kg Z axis my servo need only deliver 0.4Nm of torque to hold it up. Its a 2.4Nm (rated) servo...so I don't NEED a balance,
my servo has got plenty left over to hold the axis up AND accelerate the sh****ter out of it!! In fact I could double the Z axis mass and still not worry about the servo
being able to hold it up. Remember I just used the servos rated torque, it has three times that torque up its sleeve if needed!

Unless OPs Z axis becomes really heavy the mechanical advantage that a 5mm pitch screw offers means that even a small servo can hold the axis aloft without
breaking a sweat. You don't need either a mass balance or an air cylinder. Do the calculation yourself.....the whole point of using a screw is mechanical advantage,
you get huge thrust for so little torque.

If I put a big servo driven auto tool change spindle on my Z axis, and that is on the cards over the next 18 months or so, then I may have to revisit this decision
but at the moment neither of my spindles troubles my Z axis servo one little bit, so I don't NEED a mass balancer and unless Sus goes nuts on a spindle
neither will he.

Craig

Hi Craig
What happens when the motor is not powered? Does the brake kick in (Assuming it does not need power).
I do not want to take any risk in Z falling on my head. The most reliable way for me to guarantee that is probably a simple counter weight, but I guess this will load the motor and screw as now they have to move double the mass. The next most reliable seemed to be using constant pressure air cylinder.

Can above risk be eliminated by using motor and brakes alone?

Thanks
Sus

[joeavaerage]

Hi,

Regarding your calculation, you convert linear mass movement to a rotational momentum. During this conversion, only kinetic energy is considered. What happens to the thrust required to overcome friction of 4 linear bearings?

Relative to the thrust the frictional drag of the linear cars is near enough to zero. Think about the thrust calculation, 1Nm torque applied results in 125kg force, how much drag to you expect with each
car, 100 gram force...or even less. The linear car friction is truly negligible.


If there were a frictional component that needs be added to make the calculation more accurate I would include ballscrew efficiency, typically 97% for light-med preloaded screws.
But even including this term would change the result by a few percent at most. I elected to keep the small terms, like friction, out of the calculation because they change the result
by such a small margin and confuse the really important stuff.

In many occasions you mentioned stiffness. And stiffness is better with 32mm screws than 25mm. Given that 25mm gives you enough life span, what additional benefit can we expect from 32mm with its higher stiffness. I am just trying to understand than arguing!

Stiffness means that the machine will deflect less for a given force. Lets say your cutting steel with a 12mm endmill, and really pushing hard. The cutting force could easily be 25kg force, in which case the machine
WILL flex. The less it flexes the more accurate the cut. Stiffness is next to Godliness! The bottom line is the stiffer the machine the more accurate and the better able to contain cutting forces.

Craig

[suspension]

Got it Craig, thanks for the explanation.

There are some used ballscrews (not new-other) from ebay sellers stock. If the backslash is not present, I guess these are as good as new? Apart from baskslash, any other issue I need to worry about? I hope the accuracy does not change as it is fixed from manufacturing.

[joeavaerage]

Hi,
yes, I've seen that video, and the guy has made a very nice job.

One very interesting thing I saw in his build is he uses linear encoders for all Axes. With this, you do not derive linear position by rotational position so any in-accuracies caused by changes in lead of ballscrews are avoided. Also theoretically backslash should not be an issue as well. This way one should be able to use C7 ballscrews.

Technically that is true, but there are some considerations that make the idea a little less like a panacea.

First, if you are going to use linear scales you need a motion control system that can close the position loop with linear scales OR servos with 'load sensing' That is to say they have a regular built-in
rotary encoder and that accommodates the torque and velocity loops but the linear scale closes the position loop. Delta A2 servos can do this, approx $150 extra per servo over the B2 series such as I use.
Second, the linear scales must be good....cheap Chinese linear scales are likely less good than good ballscrews. Thirdly, there is cyclic variation in all screws, much more so in rolled screws.
The linear scale position loop does not have the bandwidth to correct the positional fluctuation that occurs with C7's. Better to pair them to C5's. Neither will linear scales help backlash. If there is lash in
a screw the lash will take up (or release) before the control system can react. The ONLY solution for backlash is to use motion components that do not have backlash. If anyone thinks they can cure lash by the
magic of feedback....good luck to them.

Load sensing linear scales is the gold standard amongst high end machines, but they use expensive linear scales and even more expensive servos and still require screws with low cyclic fluctuation, ie
C5's or C3's.

My machine does not have linear scales and I use C5 screws. I routinely produce parts to 0.02mm to 0.01mm. If I wanted better, say 0.005mm then I would have to spend many more thousands of
dollars. Ardenum is laughing that I've spent 30,000NZD, I might kill him if I spend another $15,000NZD!!!

Craig

[joeavaerage]

Hi,
as I've posted I have a Z axis servo with a brake. If the machine Estops, or the power is interrupted the brake comes on, and it locks the axis in place.
You are required to actively power the brake to have it release the armature. You might say it's fail-safe. Certainly I've never had a situation where the axis has
moved unintentionally.

Nearly all Delta servos come in two variants, one with an electromagnetic brake and another without. The brake costs a bit more. Many servo manufacturers, certainly the cheaper ones
don't have braked models so a counter balance is indicated, but as you say that doubles the mass of the axis. Having said that the acceleration calculation shows the axis mass is not SUCH a big
issue but still....

I chose Delta servos, and they have a brake, so I got one . Too easy! No shagging around here!!!

Craig

[peteeng]

Hi Sus - The brake is electromechanical. When there is no power the brake is on via a steel spring. For the brake not to work in power down, the spring would have to fail and this is highly unlikely. On power up a solenoid overrides the spring and frees the brake. Its a simple very reliable mechanism. The first two routers I made had air spring balancers, then I found brakes. Been brakes ever since. So much easier and same cost as the balancer when you add up all the associated bits.... Peter

Linear scales add a whole new dimension and cost to your build. That's very advanced hobby level and a big chequebook to get it right. Peter

Hi Nordic - Nearly any 100% solids epoxy can be used to cast surfaces. I'm sure there is a local epoxy supplier who can help. They are not exotic in any way. If you want to add a filler I recommend aluminium powder. This should be available local as well. I use Al as it can be easily machined or sanded or filed after cure. You want an epoxy with say 30-45min gel time, cures hard in ambient conditions and cures thin film... I'm sure a local boat builder supplies with west 105 can help or sika have a line in their construction epoxies. Peter

Regarding the build video - The two lands are machined in one set up but they are twisted. He does not explain how this happened (look at earlier vids). The machine that these parts where done on "should" produce a flat surface. I see that the base was bolted directly to the machine bed vs on risers. This could also be caused by the concrete still being green and changing shape. You should watch his entire series to gleen as much as possible from the build. Reality says you will have hiccups along the way.

[suspension]

Nearly any 100% solids epoxy can be used to cast surfaces. I'm sure there is a local epoxy supplier who can help. They are not exotic in any way. If you want to add a filler I recommend aluminium powder. This should be available local as well. I use Al as it can be easily machined or sanded or filed after cure. You want an epoxy with say 30-45min gel time, cures hard in ambient conditions and cures thin film... I'm sure a local boat builder supplies with west 105 can help or sika have a line in their construction epoxies. Peter

Hi Pete, what about usual concrete used for building structures? Assuming we let it cure for few months?
Also, is there any technical parameters that we must check when selecting epoxy?
Thanks
Sus

[peteeng]

Hi Sus - You need to read the Milli thread and other threads that discuss concrete. Do not use builders concrete. It expands and shrinks on cure and microcracks and macro cracks over time. The effort you put into your machine will be wasted in about a year as you see cracks appearing. Re epoxy - The easiest thing to do is get epoxy that is applicable to your application. There are too many variables to discuss concrete or epoxy in one go. Find an epoxy supplier and find out what is available. For concrete find Sika 3350 grout or similiar... Peter

[ardenum2]

Unpleasant surprise. Shipping DWH outside out Germany is very expensive. I asked for a quotation to ship to Finland and it wad 340€ just for the shipping, because it is "dangerous goods".. Then I found SKC, a similar product but they only sell to businesses, and they also said freigth costs are, quote "Very High".. So DWH is out of question and so is SKC, unless I really can't find any substitute. Dang.. feels bad to purchase a 50€ product and pay 340€ for shipping.

Weicon A seems to be something which could be used instead for precision casting. I saw CHIPLOAD on youtube use it in his lathe build.

Thoughts, any other alternatives for precision casting rail surfaces?

Diamant's website says it works with :

BEIJER OY

Elannontie 5
01510 VANTAA, Uusimaa
+358961520550

info@beijers.fi

maybe you can get it from them. If not. I'd find research papers about it, they usually give full recipes and results, a good starting point and better than walking blind.

[peteeng]

Hi Sus - So are you casting a concrete or epoxy granite machine? Plus why are you doing this? Alex CNC did all the right things with concrete (I think I have not found out what product he used) and he still had trouble after machining the lands. You are now in the philosophical position to choose what construction method to use. Why cast a huge heavy machine when you can probably make one half the weight in steel or aluminium? The machines you refer to are very large and serious machines for a hobby. A 600x300 gantry machine will be so much smaller and lighter and easier to manage.... and get the job done. Just asking.... worthwhile to contemplate what you are really trying to do occasionally... Peter


look at these- Epoxy Grouts (sika.com) I pick Sika as its an international company with product available nearly everywhere.

[suspension]

Hi Sus - So are you casting a concrete or epoxy granite machine? Plus why are you doing this? Alex CNC did all the right things with concrete (I think I have not found out what product he used) and he still had trouble after machining the lands. You are now in the philosophical position to choose what construction method to use. Why cast a huge heavy machine when you can probably make one half the weight in steel or aluminium? The machines you refer to are very large and serious machines for a hobby. A 600x300 gantry machine will be so much smaller and lighter and easier to manage.... and get the job done. Just asking.... worthwhile to contemplate what you are really trying to do occasionally... Peter

Hi Pete,
Here is my scenario. I already have a chinese 6040 router which can mill aluminum easily. This is not accurate enough and not sturdy enough. Also, to do serious cnc machining, you need various tools such as edge probes, good vices, good cutters, a BT30 like tool holders(I really need it as it is a big hassle for me to re-set Z heights after changing tools). Spending money on these seem like a joke given that my main machine - the CNC is cheap and is not accurate and not sturdy enough. So my option is either to improve the existing machine (useless in my opinion), buy a new one or build one. I really like X7 from Siyl, but 25000 is too much. So the goal is to build some thing of the size X7 which can give .01mm accuracy at-least. Syil claim their accuracy to be much better though. I will want to mill steel which can let me recover some of the costs (At-least that's what I am going to tell my wife in order justify the cost ).

Given this requirement, do you think I have other options?

regarding epoxy or concrete: I am trying to evaluate which one works for me better. I want to keep the cost down obviously.

Which of the epoxy grout do you think is suitable for my project? Sikadur®-42 HF?

Thanks
Sus

[peteeng]

Hi Sus - Here in Oz the Sika-3350 and the epoxy grout work out about the same cost. I like Sika-3350 as it has a stated modulus of 56GPa which is better than I expect most will get from EG and I can get the 3350 at the local hardware (plus I only have to add water vs mixing up large qtys of epoxy) .... I have some epoxy mineral samples at a lab for modulus test at the moment. Hopefully results by end of next week...There are always other options! but at some point, you have to jump. I usually write a list of objectives with every build to ensure I stay true to the target. Every build for me explores a different material or process. You come back to milling steel often so I suggest you forget about the high speed spindle it is a distraction. You need to solve that requirement before too much longer.... I think a fabricated steel or aluminium frame machine would be cheaper than a bulk cast machine. I also think that a steel or aluminium plate machine would do what you want. If you have a good relationship with a good machine shop they can make a plate machine that you design. C frame or gantry style. Every bespoke machine has hiccups. I've designed/built bespoke machinery for 40 years and there's always a surprise to overcome with a new one, a new process or a new material. Keep at it. Peter

The 42HF is suitable to make EG from. The three component version just adds sand. If you have a source for aluminium grit it becomes machinable vs sand. Sand and aluminium have the same modulus....

[suspension]

Hi Sus - Here in Oz the Sika-3350 and the epoxy grout work out about the same cost. I like Sika-3350 as it has a stated modulus of 56GPa which is better than I expect most will get from EG and I can get the 3350 at the local hardware (plus I only have to add water vs mixing up large qtys of epoxy) .... I have some epoxy mineral samples at a lab for modulus test at the moment. Hopefully results by end of next week...There are always other options! but at some point, you have to jump. I usually write a list of objectives with every build to ensure I stay true to the target. Every build for me explores a different material or process. You come back to milling steel often so I suggest you forget about the high speed spindle it is a distraction. You need to solve that requirement before too much longer.... I think a fabricated steel or aluminium frame machine would be cheaper than a bulk cast machine. I also think that a steel or aluminium plate machine would do what you want. If you have a good relationship with a good machine shop they can make a plate machine that you design. C frame or gantry style. Every bespoke machine has hiccups. I've designed/built bespoke machinery for 40 years and there's always a surprise to overcome with a new one, a new process or a new material. Keep at it. Peter

The 42HF is suitable to make EG from. The three component version just adds sand. If you have a source for aluminium grit it becomes machinable vs sand. Sand and aluminium have the same modulus....

The thing is working with a local shop which does not care much about precision will be a nightmare for me. Also I feel the effort to do that would be higher. Wouldn't a frame build like this need to be heat treated?
In any case, I feel the most time consuming part would be to align various rails, ball screws, etc. This will have to be done irrespective of the build is made from EG or steel.

[peteeng]

Hi Sus - Then that workshop is not the workshop to work with. I've just done a simple exercise of looking at a 200x200 solid column in Sika-3350 grout. The same rigidity column in aluminium would be 200x200x32mm thick so I could make this from plate easily. Edge bolted and dowelled. The grout column would weigh 92kg/m and the aluminium would weigh 58kg/m and be same rigidity. I can get the plate delivered to the machinist and they will machine to my models/drawings. The two shops I deal with are very fussy with accuracy to the dwgs. So I'd expect to get exactly what I designed. I am considering casting as I want to make lots of machines so casting makes sense, a single machine however needs to be thought through differently... Peter

attached is images of a Frankies saddle. Its billet machined and bolted then loctited together. Its spot on dimensionally and is the stiffest saddle I have made. Even my steel welded ones Arnt as stiff. The process scales nicely. Peter

[pippin88]

Hi Pete,
Here is my scenario. I already have a chinese 6040 router which can mill aluminum easily. This is not accurate enough and not sturdy enough. Also, to do serious cnc machining, you need various tools such as edge probes, good vices, good cutters, a BT30 like tool holders(I really need it as it is a big hassle for me to re-set Z heights after changing tools). Spending money on these seem like a joke given that my main machine - the CNC is cheap and is not accurate and not sturdy enough. So my option is either to improve the existing machine (useless in my opinion), buy a new one or build one. I really like X7 from Siyl, but 25000 is too much. So the goal is to build some thing of the size X7 which can give .01mm accuracy at-least. Syil claim their accuracy to be much better though. I will want to mill steel which can let me recover some of the costs (At-least that's what I am going to tell my wife in order justify the cost ).

Given this requirement, do you think I have other options?

regarding epoxy or concrete: I am trying to evaluate which one works for me better. I want to keep the cost down obviously.

Which of the epoxy grout do you think is suitable for my project? Sikadur-42 HF?

Thanks
Sus

Building a decent machine is a LOT of work.

If you want to make end products, go buy a better machine.

If the hobby is CNC machines, or you have a rare specific use where available commercial don't suit, then build a machine.

Spend years reading. Build a few machines.
I'm embarking on a (hopefully) high quality / premium build. I've been reading about and fiddling with CNC for 10 years. I've been looking at designs / epoxy granite / concrete etc for a few years. I've built 4 wood routers. Converted two lathes and a mill. Now I think I am ready to do a decent metal mill that will hopefully last me for many years.

To be honest, your questions show that you are not ready to build the high quality machine you want.

And us answering a few questions cannot convey all that you need to know to design and build a decent machine.

I don't mean to discourage you, but you should be aware that hobbyists building a decent machine (like the ones you have used as examples) are very rare. They cost a lot of money, and a LOT of time (years often).

You need to be aware that SYIL / manufacturers will be buying in volume, so they get parts cheaper than you can (except used, or clearance stuff). Yes, you pay for their design, labour, and profit. But when you add everything in a build up, you won't save nearly as much as you might think by doing DIY.

The little items that you may not have looked at yet add up a lot.
Decent limit switches $25 - $75 each. (2 per axis, and maybe home switches as well depending on your configuration)
Cables flexible / drag chain rated $$$
Drag chain
Enclosure $$$$$$
Electrical enclosure $200+

[suspension]

Building a decent machine is a LOT of work.

If you want to make end products, go buy a better machine.

If the hobby is CNC machines, or you have a rare specific use where available commercial don't suit, then build a machine.

Spend years reading. Build a few machines.
I'm embarking on a (hopefully) high quality / premium build. I've been reading about and fiddling with CNC for 10 years. I've been looking at designs / epoxy granite / concrete etc for a few years. I've built 4 wood routers. Converted two lathes and a mill. Now I think I am ready to do a decent metal mill that will hopefully last me for many years.

To be honest, your questions show that you are not ready to build the high quality machine you want.

And us answering a few questions cannot convey all that you need to know to design and build a decent machine.

I don't mean to discourage you, but you should be aware that hobbyists building a decent machine (like the ones you have used as examples) are very rare. They cost a lot of money, and a LOT of time (years often).

You need to be aware that SYIL / manufacturers will be buying in volume, so they get parts cheaper than you can (except used, or clearance stuff). Yes, you pay for their design, labour, and profit. But when you add everything in a build up, you won't save nearly as much as you might think by doing DIY.

The little items that you may not have looked at yet add up a lot.
Decent limit switches $25 - $75 each. (2 per axis, and maybe home switches as well depending on your configuration)
Cables flexible / drag chain rated $$$
Drag chain
Enclosure $$$$$$
Electrical enclosure $200+

I am not under estimating the effort nor difficulty in building a machine. However buying even x7 is not with in my budget. Some of yhe machines I have shown as examples are indeed built by hobbyist rather than professionals. I understand that getting the rigidity and precision is quite a challenge.

As per the costs, what I have realized is main contributors are ball screws, spindle and maybe machining. (Waiting for a quote so I will know better soon). Servos etc I am going with Chinese.. as per casing, enclosure limit switches, I have access to cheaper options so should not be a huge issue.

I've been doing CNC stuff for last 10 years and considering a better machine for almost 4 years. This is the first time I actually decided to give it a go. This would not be possible without help from forums like this.

[NordicCnc]

Diamant's website says it works with :

BEIJER OY

Elannontie 5
01510 VANTAA, Uusimaa
+358961520550

info@beijers.fi

maybe you can get it from them. If not. I'd find research papers about it, they usually give full recipes and results, a good starting point and better than walking blind.

I contacted BEIJER OY and it was them who gave me the quotation. But I will try and epoxy mixed with steel powder and see what results I can get..

Skickat från min SM-A528B via Tapatalk

[ardenum2]

I contacted BEIJER OY and it was them who gave me the quotation. But I will try and epoxy mixed with steel powder and see what results I can get.

A finnish company quoted you $350 for domestic shipping a $50 product? damn, I know the type, seen a few of these over here too. That type of an attitude results in being scratched off the list.