NordicCNC's build log

[NordicCnc]

Short update:

No progress for the last 2 weeks on the router design. I have been really busy with other projects and commitments. I had already bough 180W servos but those I already returned for some 400W servos with integrated drives. Those servos are now fitted on a Hitachi Seiki lathe (huge lathe with 400mm 4-jaw chuck) with a 1:1 ratio on the X-axis and a 2:1 ratio on the Z-axis. Ballscrews are 2005. WOW, I can now run the lathe at 10m/min without any problems. Ballscrew whip is no problem. I am very happy with that upgrade.

Anyway back to the router. Since I will be using servo motors with a 3000rpm rated speed, I thought I could take full advantage of that. I plan to do the following:

• Swap the 2010 ballscrews to 2020 on the Y-axis and X-axis.
• Swap the 1605 ballsrew to 1610 on the Z-axis
• Change gearing ratio from 2:1 to 3:1 on all axis. This will give me more torque, with lower ballsrew rpm while increasing the ballscrew pitch.
• Add belt tensioners to get more teeth engaged because of the 3:1 gearing.

This will limit the ballscrew speed to 1000rpm, and increase the Y- and X-axis maximum feed rate to 20m/min. Z-axis feed rate will stay at 10m/min. I feel like this is a better idea than trying to spin the ballscrews at 1500rpm with the 2:1 ratio. I want to take full advantage of the servo motors RPM.

On another note I was planning to use 400W (maybe even 750W) Delta servo motors, with dual motors on the Y-axis. I need to do some calculations if it would be a good idea to go for 750W. Anyway I saw on YouTube that there is a auto tuning function available in the software but I am not sure how to tune the dual motors on the Y-axis.

1. What do you guys think about the increased ballscrew pitch, 3:1 gearing and belt tensioners?
2. Is it possible to auto tune 2 motors at the same time?
3. Perhaps I could change the design and use only 1 servo motor on the Y-axis with belt drive connected to both sides. This in turn will not allow for squaring the gantry with motion controller but I think i can get it square any way.
4. How wide can the gantry be without having to use dual slaved Y-axis motors?

[NordicCnc]

So machine design is now what I consider 99% completed so that I can start ordering parts. Since none replied on the ballscrew change I've decided to do the following:

- Keep the 2:1 ratio
- Change Y- and X-axis ballscrews to 2020
- Keep the Z-axis ballscrews as 1605
- No belt tensioners
- Double Y-axis motors will be used


I will put together a shopping list for all components so that I can get as much as possible in one order without missing anything. The final piece of design was to find a good location for the Y-axis home/limit switch. Cable chains I will fit later and wont add those to the 3D at all. Please ignore that the screw is not in the center of the limit switch. I will lathe and mill some custom screws but I could not care to design those yet.



Final assembly!



Some things still bugging me is the 120x80 for the gantry. I hope that those will not be too weak for machining aluminium with the ATC spindle. I am still consider changing to 160x80. JAZZ, if you read this, I remember that you wrote somewhere that for larger machines you use the 160x80 for the L-shape gantry. Since my gantry is 1200mm wide and I am using an ATC spindle, would it be wise to go for 160x80 anyway?

[joe.ninety]

Can I just ask what the benefit is of using blocks of profile to sit the gantry profile on, as indicated in the picture?



It seems because of this you were forced to place the bottom linear rail on the front, thereby pushing the spindle further away from the gantry. I'd always though that the idea is to try and keep the centre of gravity of the spindle as close as possible to the bearing blocks the gantry rides on.

This is not in anyway meant to be a criticism, but just me trying to understand if this design means there are benefits to it that outweigh the spindle being pushed further outward.

Cheers

[mekanik]

As a rule you ideally want the spindle IN the same envelope as your X axis bearings, i would make the distance between these bearings further apart.

[NordicCnc]

Can I just ask what the benefit is of using blocks of profile to sit the gantry profile on, as indicated in the picture?



It seems because of this you were forced to place the bottom linear rail on the front, thereby pushing the spindle further away from the gantry. I'd always though that the idea is to try and keep the centre of gravity of the spindle as close as possible to the bearing blocks the gantry rides on.

This is not in anyway meant to be a criticism, but just me trying to understand if this design means there are benefits to it that outweigh the spindle being pushed further outward.

Cheers

Those block are used to increase the gantry clearance. I want to build machine out of aluminium profiles and the 200x80 profile for the Y-axis sides are not high enough. Also by placing the linear rail on the front of the X-axis will allow me to use the work area fully, without increasing the footprint. If I were to put the linear rail on the bottom of the gantry profile I would lose approximately 160mm in the X-axis travel.

You are right about the overhang, but I would claim that it is not that critical. As long as the Z-axis and gantry is stiff enough, it should not be any problem at all. If you check other builds, the overhang is similar!

Thanks for your comment.

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[JAZZCNC]

Ok well I'll answer this question seen as he's mostly following my design.!

It always makes me smile when I see comments like these because while the physics shows that what you are saying is the ideal location the reality is that it makes no difference to the machine and how it works.

To prove this point I'm going to give you a challenge.! . . . Industry demands the highest cut quality and performance, so logic dictates that they would follow the physics and optimum location very closely.?

So go find me a machine from the major manufacturers that place the spindle smack between the bearings.! . . . If you find one then I guarantee you'll have seen ten before it that don't.!! . .. In fact, you'll be lucky if you find any with spindle inside the bearings.!

You all need to stop worrying about the physics and virtual world so much and get building so you can realize just how little if at all, these affect a real-world machine.!

Exhibit: A

Can I just ask what the benefit is of using blocks of profile to sit the gantry profile on, as indicated in the picture?

It seems because of this you were forced to place the bottom linear rail on the front, thereby pushing the spindle further away from the gantry. I'd always though that the idea is to try and keep the centre of gravity of the spindle as close as possible to the bearing blocks the gantry rides on.

This is not in anyway meant to be a criticism, but just me trying to understand if this design means there are benefits to it that outweigh the spindle being pushed further outward.

Cheers

To answer you directly Joe, then to place the gantry further back to bring spindle into line with bearings would actually weaken the machine not make it stronger. To do what you suggest without getting into complex gantry side designs means using plates for gantry sides that can flex side to side and introduce vibrations at the tool.
I can tell you from building many different designs of router that the design he's using is the best possibly way to build a router without getting silly about.
Mike is correct in that having longer distance between the bearings is good but thats a trade off between travel and foot print of the machine. In the grand scheme again it makes very little difference.

As a rule you ideally want the spindle IN the same envelope as your X axis bearings, i would make the distance between these bearings further apart.

[NordicCnc]

As a rule you ideally want the spindle IN the same envelope as your X axis bearings, i would make the distance between these bearings further apart.

Can you explain what you mean? I am not sure I follow.

Edit: I think you meant the spacing between the Y-axis bearings? Doing this would also decrease the Y-axis travel. I also want to be able to machine dovetails at the end of the table, so overtravel is a must!

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[mekanik]

I was working on the assumption X was your Base and Y your Gantry, Dean is the go to man for advice and if he says it's OK just crack on.
Regards
Mike

[NordicCnc]

I was working on the assumption X was your Base and Y your Gantry, Dean is the go to man for advice and if he says it's OK just crack on.
Regards
Mike

I see! My design is defined with Y-axis on the base frame, X-axis on the gantry and then Z-axis on the spindle. Anyway thanks for checking in!

[NordicCnc]

I have started thinking about precision tools that I will need for the build. I have a post already on the forum where JAZZ explained the tolerances very well: http://www.mycncuk.com/threads/13435...hinists-square

I already own a good dial indicator so now I need a set of straight edge and/or machinists square.

1. Do I need both a straight edge and a machinists square, or would just a machinists square be sufficient?
2. What straight edge length is required? Linear rails are 1500mm (Y, base frame), 1200mm (X, gantry) and 500mm (Z).
3. What machinists square dimension (height x width) is required? Linear rails are 1500mm (Y, base frame), 1200mm (X, gantry) and 500mm (Z).

Helios Preisser straight edges:

1. Steel square straight edge, cross section 40x8mm, length 1000mm, DIN874/2, @44,40€ https://online.helios-preisser.com/p...1050432013%5D)
2. Stainless steel square straight edge,cross section 40x8, 1000mm, DIN874/2, @98,00€ https://online.helios-preisser.com/p...4973167720%5D)

Helios Preisser machinist squares:

1. Steel square with base, cross section 30x5mm, length of beams 1000x500mm, DIN unknown?, @57,00€ https://online.helios-preisser.com/p...1027812493%5D)
2. Steel square with base, cross section 50x10mm, length of beams 1000x500mm, DIN 875/2, @165,00€ https://online.helios-preisser.com/p...4525824975%5D)
3. Steel square without base, cross section 30x5mm, length of beams 1000x500mm, DIN unknown?, @24,50€ https://online.helios-preisser.com/p...0938670859%5D)
4. Steel square without base, cross section 50x10mm, length of beams 1000x500mm, DIN 875/2, @135,00€ https://online.helios-preisser.com/p...0456342882%5D)

So many options, but I think that the DIN874/2 and DIN875/2 would be sufficient. Then it is only about with or without base and the length?