where to start?

[trounce]

One last question before I get designing....


As you can see by this image the sheets of 8 x 4 I'll be cutting get used almost right up to the edge of the wood. I will obviously need a frame which is larger so the router will be able to travel past the edge of the wood, I'm thinking 9 x 5 does this sound about right?

[JAZZCNC]

JAZZCNC you have given some excellent advice in this and other threads and I am sure that myself and others will benefit for your experience.
A question, how does rack and pinion compare to ball screws in repeatibilty and accuracy, and does the pinion ever jump teeth under load?
Sorry if this sound dim, but curious.

Well Jim the honest answer would be they don't compare.! Infact if you asked me too place each system in numerical order of effeiciency, repeatabilty and accurecy then R&P would probably come 4th. . . . 1st ballscrews, 2nd lead screws close 3rd belt drive then R&P.!!

That said it's doesn't mean it's rubbish and for large format machines doing lower precision jobs but with high loads and cutting feeds then it's usually the best option.

Ballscrews (and Lead) are too whippy over long length's without taking special measure's IE: rotating nuts or excessive sized screws,(which brings other issue's) plus the accurecy and precision they produce hisn't often required for cutting wood and plastics etc which most large format machines are used for.

Belts are very accurate, effiecent with very good repeatabilty, virtually no backlash. But again they have there issue's over large length's and don't handle high loads as good as R&P. They can be made do-able for large machines but not ideal . . . More suited to large machines with low loads and high speeds.

So IMO R&P is the best all round option for a large format machine with high loads (IE: heavy gantry,deep DOC) needing medium accurecy with resonable repeatabilty and high-ish feed rates. . . Perfect for Cutting wood, plastics, stone.

Regards jumping It's not an issue if designed correctly with correct alignment and pinion tensioning into the rack. The issue's can come from debries getting in-between the rack & pinion but if the rack is positioned with the teeth facing down with the pinion engaged by spring loading into it rack from benneth and positioned out of the firing line as much as possible then it's not an issue normally.
The trick is getting the tensioning just right so it's not so weak it allows teeth too jump or have excessive backlash but at the same time not to high cause's binding which helps to reduce backlash (too a point) and jumping but cause's excessive wear. The required tension will vary from machine to machine depending gantry weight, cutting forces etc and a little setup & adjustment will be required at first but ounce setup it works good for this size an type of machine.

Again at the end of the day it's horse's for course's.! . . . . If you want super precise get a show jumper(screws), if you want light weight and speed get a stallion(belts), if you want a good strong all round work horse then get a shirehorse.(R&P) . . . . . If you want an old knackerd Donkey get some threaded bar and MDF. .:whistling:

[trounce]

Edit: double posted in error

[m.marino]

Yep a very good post and one which is very wise to listen to. I am right now designing machine number two (first was a kit) and wishing I had built from the start. Though I have learned a lot and the machine is right now cutting parts to be sold which is paying for itself slowly.

Ask tins of questions. Get access to a CAD program (I would suggest ViaCAD as very affordable for the quality/support you get) or a lot of sketch paper and draw every detail out. Work it out then post it here and ask more questions. Trust me there is more then enough folks here who A) really know what they are talking about and B) really will try to help you get a good build for the money you put into it. Just remember that building slowly and with totally ridge mentality to precision will pay off for a very long time.

Best of luck and keep going.

Michael.

[luke11cnc]

Michael Viacad ??

is it Viacad punch I need??

what version are you using

how much did you pay for it??

James

[m.marino]

James,

I am using ViaCAD 2D/3Dv8 and bought it during the pre release ($69). You can get it now for $99 on their site and might be able to get a discount of 15% (I don't know if it is still running). It is a really useful program based on the ACIS modelling core (Same core as SolidWorks). No it is not at that level as it is also not at that price, but for a good MCAD/ACAD program that will get a lot done with excellent forum and support via that forum it is very hard to beat. Comes with videos and pdf user manual (that needs updating in places and they do know and are working on it). The drawings you see my putting up in the forums now on my build are done by ViaCAD. That plus a good CAM and your set on that side of things (CamBam, Aspire, and a few others come to mind). Trust me you don't want to cut corners on software or you end up editing a lot (don't ask how I know).

As to the OP good luck and keep going it takes time and doing it right is worth the time taken. Trust me I know that one the hard way.

Michael

[JAZZCNC]

Hi Neil,

Those tools are more than enough in the right hands.
Regards the box 50x50 3mm wall is Ideal and cost affective.

The size of machine you want I started to design for a guy a year or so ago and to do pritty much the same panel work. The budget was tight on this as well but didn't want to build weak.
It was decided steel frame and R&P was the best way to go. Often most designs requires driving the X (or long) axis from both sides and this means extra expense, 2 motors, 2 drives,larger power supply etc.
So I started designing so I could build it with just 1 larger motor on the long Axis 3:1 ratio giving roughly a 25mm pitch thou can be changed with differant sized pulleys and/or pinion.! . . . The pics below are as far as I got. (As folks are probably gathering by now I like my pics.!!. . . They tell a thousand words. :tup:)

It's just a rough layout design and still needs plenty more work but the frame etc are all to scale thou a little extra strengthening to the bed and some bracing are still required. The dimensions are 3mtr x 1.5 which is more than enough for 8x4 sheets.
It never got built due to the guy being made redundent and it's currently on hold untill another day, hence I stopped designing.
If you want to know more drop me a PM and I'll give ya my number.

Also digging this out got me thinking how much the steel would be for this frame and If it could be built for £1000.???
So I rung my supplier and got a price for 50x50x3 7.5mtr lengths of £25+Vat . . . I've worked out 6 lengths lengths of box section should be more than enough. . . so £150 will build you the base frame and gantry.
Commercial Rack is roughly £30 for 2mtr lengths so £120 for X&Y axis, pinions £8 x 3 shaft say roughly £20, Bearings and pulleys approx £50 so R&P for X&Y Axis approx £220-50.

Throw in roughly another £300 for linear rails and you still havent got Z axis or motors, drives, PSU etc . . . so what I'm saying is on reflection then £1500 is more than likely your finished price. thou for £1500 you'll have a cracking machine.

[trounce]

Hi Neil,

Those tools are more than enough in the right hands.
Regards the box 50x50 3mm wall is Ideal and cost affective.

The size of machine you want I started to design for a guy a year or so ago and to do pritty much the same panel work. The budget was tight on this as well but didn't want to build weak.
It was decided steel frame and R&P was the best way to go. Often most designs requires driving the X (or long) axis from both sides and this means extra expense, 2 motors, 2 drives,larger power supply etc.
So I started designing so I could build it with just 1 larger motor on the long Axis 3:1 ratio giving roughly a 25mm pitch thou can be changed with differant sized pulleys and/or pinion.! . . . The pics below are as far as I got. (As folks are probably gathering by now I like my pics.!!. . . They tell a thousand words. :tup:)

It's just a rough layout design and still needs plenty more work but the frame etc are all to scale thou a little extra strengthening to the bed and some bracing are still required. The dimensions are 3mtr x 1.5 which is more than enough for 8x4 sheets.
It never got built due to the guy being made redundent and it's currently on hold untill another day, hence I stopped designing.
If you want to know more drop me a PM and I'll give ya my number.

Also digging this out got me thinking how much the steel would be for this frame and If it could be built for £1000.???
So I rung my supplier and got a price for 50x50x3 7.5mtr lengths of £25+Vat . . . I've worked out 6 lengths lengths of box section should be more than enough. . . so £150 will build you the base frame and gantry.
Commercial Rack is roughly £30 for 2mtr lengths so £120 for X&Y axis, pinions £8 x 3 shaft say roughly £20, Bearings and pulleys approx £50 so R&P for X&Y Axis approx £220-50.

Throw in roughly another £300 for linear rails and you still havent got Z axis or motors, drives, PSU etc . . . so what I'm saying is on reflection then £1500 is more than likely your finished price. thou for £1500 you'll have a cracking machine.

If you don't mind me asking, where can I find the rack at that price? I've been googling away and only managed to find some on ebay for £56 a metre, I must be looking for the wrong stuff :cry:

[JAZZCNC]

WMH transmission . . . Here you go. http://www.wmh-trans.co.uk/Products/...K_MATERIAL_EN8

[Jonathan]

If you don't mind me asking, where can I find the rack at that price? I've been googling away and only managed to find some on ebay for £56 a metre, I must be looking for the wrong stuff :cry:

This is the place:

http://www.wmh-trans.co.uk/

I got my steel box section from Adey Steel. Good prices but not sure what postage would be if available...

Edit: Looks like Jazz beat me to it...