DIY with quality components

[yohudi]

Totally revised machine spec and can now attach pics so I've edited this original starting post... see big post later in this thread

[ger21]

Where's the pics??

Most people usually use the same motors and screw pitch on both X and Y axis. It's not a requirement, though, but if you're buying new, why are you choosing different components?

Were you planning on direct driving the rotary axis?

[Halfnutz]

It sounds awesome, but I wouldn't want to have to write the check for the linear rails. Have you got prices for them yet? I'm curious as to what rails that long would cost new. I have seen them on ebay that long, but even there they were a couple of grand a pair. I picked up two 9.5 ft. THKsr15 rails and six trucks and a web belt and pulley system on ebay for three hundred, but the heavy rails are so much harder to find and so expensive.

Another thing you need to consider is the length of those ballscrews. If you try moving long screws fast they have a tendency to whip I understand. I dont know if yours are two long or not, but its something to check out. Its why people tend to go other routes, like rack&pinion or belt/pulley on machines with that much footprint. Ive seen ballscrews used, but they were very large and very expensive.

If you've got the budget it sounds great. What about the pic's you mention?

[yohudi]

Gr21
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I'm buying new components for the X+Y Ballscrews, All motors and controller but the Z Axis and the A Axis are pre-assembled items.. so I'm trying not to destroy them through inexperience.

A lot of these items are sourced from ebay and the like.. so you can't always pick and choose what you get. Hope this clarifies things.

I was planning on direct driving the rotary axis. If you check the pics of it you can see that it has a servo motor direct driving it at the moment. Is not that clear in the picture but it has a built in planetary gearbox. I hope to mount the pinion off the servo motor onto a stepper of similar characteristics and ...fingers crossed... it will perform just as it did in the first place. If worst comes to worst I will sort out an alternative means of driving it indirectly. As I said I'm still new to this game and learning all the time...

Halfnutz
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I've already bought the items on my list that do not have * next to them.. prices can vary a lot.

The Z Axis assembly in the pics cost me £ 153...
Rotary drive for the A Axis cost £ 17..
X and Y rails and guides ... paid about £ 270 to £290 for each complete set.

I priced up just the Hiwin guides new in the UK and for Guides without Rails it would have cost over £360.. and the 2500 mm rails would have cost at least the same as the guides and probably a lot more.

got to dig.. but it's worth it

again pics are here

http://www.cnczone.com/gallery/showg.../24752/cat/500

[Halfnutz]

Thats great! Less than I would have thought, but not cheap. I have these 9.5 ft SR15 rails (about 2800 mm ?) that I got for a song, and I also have a pair of SR15's 6 ft long for the Y axis, but I dont know if they are heavy enough (I'm going to try them at some point anyway). They came off of a commercial vinyl cutting machine and include a really nice belt drive set up. I am also going to build a large format gantry with them someday, but I've got too many other projects going on at the moment, and I am not sure of where I want to put the thing yet. It will be welded square tubing and not easy to move once its built. My workshop is so packed....

Good luck, I'm anxious to see your progress as it develops, it looks like your off to a great start..

[yohudi]

Halfnutz
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Appreciate your comments.. thanks.

So far have saved quite a bit of money on components. Thinking is that savings will offset the cost of some of the pricey parts that I want to buy new. Don't want to take a chance on used Ballscrews and Ballnuts etc.. but at the sizes I need they are quite expensive.

I meant to reply to your remarks about screw whipping earlier. This is a big concern with me and it's why I'm hovering around the Motor/Thread issue like a big nancy.. just don't want to get it wrong and bend something that costs a packet. Will most likely choose a motor/screw combination that leans towards under-driving rather than over-driving the X Axis. Not looking for many 100's of IPM out of this to start with and can always upgrade it at a later date. Accuracy and reliability are my main concerns. I plan to buy the biggest and best X Axis Ballscrew I can afford and treat it like a baby.. until I know what the limits are etc...

[ViperTX]

ger21....."Ah, the pitch for X and Y axis are the same.....5mm...."....aren't they.....Motors are basically the same aren't they....one is has a bit more torque....but if it has the same number of steps as the other.....it's basically the same....

[ger21]

I saw that the pitch was the same... was just curious as to why the different diameters, but I didn't realise they were from Ebay.

[jeffs555]

I don't know what travel rates you need, but you definately need to double check your calculations on the ball screws and steppers. Might be ok, but there is a reason most large machines use servos and rack or belt drive. If you plan to use this machine for a business, time(ie speed) is money.

Depending on what type of bearings you have on your ball screws, the maximum speed for your X axis without whipping will be somewhere between 1500 to 3000 mm/min.

The steppers might also have a speed problem. The torque curves in the Sanyo data sheets are with a 100v power supply, so with 65 volt max drives, your speed will be almost half of that in the curves. Even at 100v they might be too slow.


PS Whipping is not the only problem with long ballscrews. Longer and larger screws have more inertia, so acceleration and deceleration when changing direction are slower. You can download a free motor sizing calculator here. http://www.parkermotion.com/scripts/..._downloads.asp (look for sizing and selection tools)
This program lets you put in screw and machine characteristics including desired speed and acceleration, and outputs a graph of the torque curve required.

[yohudi]

Originally Posted by jeffs555 I don't know what travel rates you need,...... the maximum speed for your X axis .....will be somewhere between 1500 to 3000 mm/min. The steppers might also have a speed problem. ......with 65 volt max drives, your speed will be almost half of that in the curves. Even at 100v they might be too slow.

jeffs555
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Thanks for your interest.

Regarding speed:

1.5 - 3.0 Metres per minute sounds relativly low speed for machine this size.. I hear what you are saying.. motors are under-driven at 65v also. I thought of both of these aspects which is reason for this post ... to check my thinking and conclusions.

I'm happy to under-drive to start with. Last thing I want to do is push the Ballscrews too far and encounter whipping and bending problems. Accuracy and reliability are my main watchwords at the moment.. saw a tagline/sig on the forum... can't remember who has it.. but says "1st get good.. then get fast !!". Sounds like good advice to me.

Will be business usage for this machine and time is money as you say. I'm a bit of a one-man-band operator and I will have finishing and assembly work to get on with while CNC cuts my work for the next job. If it only cuts and shapes as fast as I could by hand then it will improve my job turnaround times by 100%. I think it should go well beyond my hand-working speeds so will still be worth the investment.

Long-term I am thinking about upgrades to both Ballscrews and motor drive. but to my mind I need to test and prove the rigidity of my frame design in real work situation first. I've never built anything this big with 8020 type extrusion. No good to me if forces exerted make it sway and slop all over the place... so softly softly catchee monkey is my planned approach.

Thanks again for your input.. this is just what I need really.. before I buy items and commit myself to a dodgy plan. I do take all comments on board for serious consideration.... so please keep them coming

[ger21]

A 2HP router is on the low side for 3M/min feed speeds, if you're cutting 19mm panels in a single pass. I'd say use no less than a Porter Cable 7518. Tooling plays a big part in this as well. On our commercial machine, with chipbreaker spiral tooling I can cut 19mm plywood at 10M/min, but with insert tooling I slow down to 3-4M/min, or risk breaking the tool. This is with a 10HP spindle, btw.

You might also want to look at higher lead ballscrews, 10-20mm instead of the 5mm you mentioned. This will reduce whipping, and keep the motors spinning slower where they have more torque.

[yohudi]

Originally Posted by ger21 A 2HP router is on the low side for 3M/min feed....19mm..use no less than a Porter Cable 7518. Tooling plays a big part...... You might also want to look at higher lead....10 - 20 mm ..... This will reduce whipping, and keep the motors spinning slower where they have more torque.

ger21
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Re: Spindle/tooling

Noted your remarks ...at this point in time I have no real reference or experience to make a decision without the kind of advice you offered. I appreciate the tooling issues so I'll definitely adjust plans with this in mind.

Re:Thread

Big thanks for sharing information above.. again this is exactly what I need... The cost increase for 10 mm or 20mm lead screws is within my budget and as you pointed out this would reduce motor speed and therby keep me in the higher torque ranges of the motors.

Also with under-driven motors this makes even more sense to me. I will get the most out of them with lead /thread as you suggest and this will also stand me in good stead for whipping avoidance.

Thanks for your sound advice