Reducing the space in my garage.

Hi all,

I thought I’d better introduce my build and thank all those that have contributed to this forum, it’s helped my a lot already.

I should own up to the fact that I have started my build. I was having trouble getting my head around the challenge, so started mocking up an idea with bits of sheet material I had hanging around.

The design started in sketchup, I will post it up on the site once I have found a host.

I’m quite a practical person, but I know my limits, especially when poking a stick into an electrical circuit. If I could borrow from your collective experience, that would be great.

Here’s the outline, photo’s to follow.

The machine will be used for profile cutting sheet materials using a drag knife or a small router. It’s for personal use, so no more than 10 operating hours a week. The cutting area is 1600mm x 800mm, with 100mm clearance between the gantry and the cutting table. The main material to be cut is natural wood nothing too hard – mostly European species, circa 1600 on the janka hardness scale. I will be aiming at a feedrate of 8m/min.

My target resolutions are 0.1mm the X and Y axis and 0.05mm on the Z-axis. The Z-axis is the priority. I appreciate they are not considered particularly tight by the standards found in this forum.

Although I had read and viewed as much as I could before starting, the technical stuff takes a while to sink in, so the machine was designed with http://www.cncroutersource.com/ as the main reference point. It’s a great resource for beginners like me, although I have made a mistake with the position of the gantry over the X-axis carriages. If the machine works, I will correct this.

Frame
The frame has been built using dexion bought from the local scrap yard. The frame sits over and will attach to a woodworking bench while the machine operates, borrowing mass and stability. The table is made from mdf, its a torsion box. Dexion is being used internally and externally to create the structure. The mdf used isn’t the moisture resistant type.

To hold work down, I’m thinking t-nuts for two thirds of the table, one third vacuum.

Gantry
The gantry has been constructed, it is 10kg and when I give it a shove, it runs three quarters the length of the X axis. Its dimensions are 1200 x 50 x 150mm. Made from two lengths of aluminium box section 50 x 50 x 3mm, they have been spaced by and bolted to an extruded aluminium I- beam, 50 x 25 x 2mm. The design flowed from what was available from the scrapyard at the time, bearing in mind the designs I’d studied online; 3mm is a little light for creating stable joints in aluminium, steps have been taken within the design and will be taken within the final assembly.

The ends of the gantry are connected to aluminium plate, which make up one face of a torsion box that connects to the carriage running on the X-axis.

Z-Axis
The Z-axis is a box wrapped around and over the Y-axis, think ‘Joe’s CNC’. Drive is at the rear, which I appreciate is sub optimal. I’m assuming this will introduce additional wear and could lead to binding. The front and rear plates of the box are made from 6mm aluminium plate. The box is 170 x 89 x 230mm.

A Tr 12 x 3 trapezoidal screw made from steel C45, with a derilin antl-backlash device will provide motion to the Z-axis carriage. Tr 12 is much more than I need, but is defined by the backlash device. The screw will be fixed and supported. The spindle will be supported at each end by 6mm aluminium angle. I've looked a micro-leadscrews, but dismissed this option.

The Z-axis will be belt driven, no reduction. I will be using 2 x 15 tooth T5 pinions, providing the 6 tooth engagement required and a polyurethane timing belt, 280mm long. The requiring a centre distance will be102.5mm.

Linear Rails
At the time, and without the benefit of the information contained within this forum, cheap linear motion was the main stumbling block. I went with Makerslide, which might be considered unfortunate:

http://www.mycncuk.com/threads/6569-...ght=makerslide

The Makerslide has been mounted horizontally on two dexion rails that make up each X-axis. The rail has been mounted in parallel on the each vertical face of the aluminium box section that make up the Y-axis. The Z-axis consists of four sections of Makerslide, two sections working as rail attached to a carriage made from 6mm aluminium plate, two sections acting as structure for the router/knife.

The X and Y axis solidly resist the forces and moments of inertia described by cncroutersource when tested firmly by hand:

http://www.cncroutersource.com/do-it...NC-router.html
http://www.cncroutersource.com/build...nc-router.html

The Z-axis needs a little more work to make it completely solid. I will create a pattern, against which I can tighten and lock off the v-wheels on the carriage.

If I keep the rails clean, then hopefully the main issue will be wear.

Visiting the scrapyard the other day I pulled out a section of V-track (US Patent), 2 meters or so long, made of carbon steel. They may well become part of the design, dependent on the rate of any wear.

Motion
The intention is to drive the X and Y axis using reinforced timing belts, per Mike Everman

http://bell-everman.com/products/lin...elt-linear-sbl
http://www.cnczone.com/forums/linear...-ever-say.html

The belt to be used is Brecoflex T5 10mm steel reinforced belt. The system requires reduction, circa 3:1, over above. The gearing for the X-axis will be boxed in within the ends of the gantry protecting the exposed belt from debris, I have some work to do to find the parts at ‘beltingonline’, to make the gearing fit.

http://www.cnczone.com/forums/linear...er-say-14.html
http://www.cnczone.com/forums/linear...er-say-20.html

Per the above thread, the gap between the upper belt and the rollers must be held at 0.05 -0.1mm. and the belt must be seated within a channel preventing it track laterally. Resolving these two points has not been too problematic. I have a few more hours on the X-axis before it is finished, I will be using four UHMWPE pads to reduce the reliance on bearing.

In the real world the end result can looks something like this:
http://www.youtube.com/watch?v=SpIuQ...KmL6gQvVQ-GvWw
http://www.youtube.com/watch?v=T9QU3YQe-Sc

Does anyone here have experience of the Bell - Everman approach?

Drive
This feels tricky. The recommended approach is 3Nm, Nema 23, low inductance motors, ideally run at 65-70Vdc on 75-80vdc drives.

The motors I have in mind are: www.cnc4you.co.uk/index.php?route=product/product&path=83_84&product_id=364 . For what I have in mind, I suspect it is preferable to set up the wiring in series i.e. high torque/low speed.

I’m still considering what steppers to use. I understand, 1/8^th micro-stepping should be sufficient for my needs. I still have a little time in hand before I need to raise the funds.

Power supplies, the options are between regulated and unregulated supplies. It looks like unregulated supplies are better suited to deal with fluctuating loads. More reading required on this so I can gather the right parts.

Control
BOB. I’m currently looking at the OPPB V3. A four axis controller offering the required 25KHz step frequency and 10A (80% total) load requirements, if wired in parrallel. Running 60Vdc means I would lose some functionality. It is built with MACH 3 in mind. More reading required.

Mach 3, I’ve used the product briefly in the past. It has a forum for support not provided by the manual.

So, even without the addition of photographs, it might sounds like there are a lot of weaknesses in the choices I have made to –date. At this stage, I’m not overly concerned, as it takes time to build the skills and insight required. The hope being, when it come to building v.2, I will have all the parts and skills required to build a much stronger machine.

Thanks in advance for any comments!
Rich

Table design using dexion and images of the build so far.

The front plate of the z-axis is currently made from 2 x 3mm aluminium plate. The final build will separate these two plates, increasing stiffness and absorbing vibration., I will use sheet ply and a vibration dampening material.

If this version 1 will suite your requirements why build version 2 ?
If you think it might not suite your requirements then go straight to verison 2 now. After reading your post I would go straight to version 2.

Thanks Eddy. I did give that issue some thought. I decided to factor in my own in-experience and concluded that I would carry on building this slightly fragile machine first. I may need to cut plate aluminium in the future, hence the need for v.2.

Spent last evening reading the support offered by Gecko: http://www.geckodrive.com/support/st...or-basics.html . It offered a very helpful understanding of why unregulated supplies are preferrable i.e. motors behaving as alternators. On a three axis machine, using 4 x 3.1Nm motors (CNC4YOU) in parrellel, the numbers appear to be 11.088 amps and 57.25 volts. The numbers on power requirements will need double checking, they seemed low.

Anti-backlah Nuts
Is this a good buy: http://www.damencnc.com/en/component...--spindles/101

I was originally looking for something that worked with a Tr10 x 3, but I have been unable to find a workable solution, other than the MDL-2-TR 10x2D Special Nut, sold by Merchant Dice:

http://www.ebay.co.uk/itm/CNC-Z-Axis...item483f9663e7

Igus do these, I expect them to be top quality coming from them

http://www.igus.co.uk/wpck/2371/dryl...zgewindemutter

Quote:

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Originally Posted by Rich

On a four axis machine, using 3.1Nm motors (CNC4YOU) in parrellel, . . .

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Did you mean a 3 axis machine with 4 motors ?

Lol - yes, I'll edit. Thanks for the link!

Spent last week tidying up the gantry, fitting flange bearing and reading, mostly about stepper motors:

http://homepage.cs.uiowa.edu/~jones/step/an907a.pdf
https://www.mpja.com/download/18304ms.pdf
http://www.haydonkerk.com/Portals/0/...uators_101.pdf
http://www.selene.co/Blog/2011/08/se...motor-winding/
http://www.micromo.com/microstepping...-and-realities

The aim was to understand how the choice of motor i.e. chopper motors, effects the design of the circuit. Without the depth of knowledge to fully understand everything I have read, there where a number of points I need to carried forward:

(1) Motors can be driven at between 10-24 times there specified voltage. Increasing the multiplier will increase the stiffness of the motor.
(2) A motor is most effective when is it operating within the 'slew' range of the speed torque curve.
(3) Micro-stepping increasing the machines efficiency at the expense of the available holding torque.

The last point is important as it helps limit my expectation of micro-stepping i.e. it won't make up for accuracy lost within the design or the build ) I would imagine this last point is reflected in the 'motorcalcs' spreadsheet, which includes a significant safety factor?

Quote:

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Originally Posted by Rich

The last point is important as it helps limit my expectation of micro-stepping i.e. it won't make up for accuracy lost within the design or the build ) I would imagine this last point is reflected in the 'motorcalcs' spreadsheet, which includes a significant safety factor?

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From what I've read, 1/8 microstep seems to be the most popular and is a good starting point, that's what I use anyway and it's working fine.

Thanks Eddy, that helps with my working out.

At 8 microsteps the resolution using a pinion with a pitch diameter of 23.87mm is 0.0149mm, and that is good enough for me ) But the holding torque is reduced to 19.5% peak value, per the linked paper. However, with a gear ratio 2.8, holding torque is increased to 54.6% peak value. It seems to follow when the gear ratio is include that 4 microsteps provide a resolution of 0.0106mm, with no loss of holding torque.

Quote:

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Originally Posted by Rich

At 8 microsteps the resolution using a pinion with a pitch diameter of 23.87mm is 0.0149mm, and that is good enough for me )

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Nope you forgot the to include mr Pie.!! . . . .23.87*pi=74.989 /1600=0.0468

Also you shouldn't really think of Micro stepping in terms of increasing resolution. It has more affect making motors smoother.
If you need resolution then best to achive it by lowering the pitch.

Regards voltage then you can easily run those motors above the guide given on Gecko site. They easily run at 68Vdc without any trouble and the extra voltage gives that bit more torque and speed.
The amp you'll require will depend slightly on the type of PSU used. With Unregulated toroidal supply you'll only need aprox 60%-70% of total rated motor amps. IE: 4 x 4.2a=16.8 / 65%=10.92A

Thanks for those three points Jazz, they help a lot!

I've corrected my calculations and marked them down as 'guidance only'. The main issue I was focused upon within the calculation was the effect of microstepping on the available holding torque. It appears with a 2.8 gear ratio, set at 4 microsteps, the machine retains 100% peak holding torque.

Having used your original recommendation as a starting point for the research, I now see that I have the option to spec the machine according to what is required, circa 1.5Nm Nema 23 low inductance or over spec the machine and carry the electronics forward. More reading to be done!

Don't forget to take into account the screw pitch, it's the resolution at the tool you want to calculate

On the z-axis using a TR12x3, resolution will be 0.015mm at 1 microstep. This assumes no backlash, deflection of the carriage or issues with the table. If I'm out by a factor of 10, then the starting point would be 0.15mm. As the majority of any variation will arise as a result of deflection, the option to gear the z-axis is on hold.

The z and y axis are belt driven, the gear ratio is 2.8, so the starting point for mechanical resolution at 1 microstep is 0.1339mm. I will have issues with positional accuracy when cutting longer lengths, but I can compensate within Mach 3.

I'm guessing you started you build with better figures?

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Originally Posted by Rich

I'm guessing you started you build with better figures?

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I didn't calculate them as such but obviously had an idea of what I needed. I used the best components I could and the best design I could build myself with the tools at hand. Having plenty of engineering experience I knew it would be achievable, but having no experience with cnc, I initially relied heavily on the advice from members of this forum on the mechanical side.

The actual figures after the machine was finished are here; http://www.mycncuk.com/threads/7155-...6572#post56572
that is with a 200N force applied as described.

Great number Eddy. Your log is one of many logs I have been reading )

So after further research I found this website:

http://www.orientalmotor.com/support/motor-sizing.html

The numbers offer a guide to the amount of torque required to move at specific feedrates.

The issue now is what will the available torque curve will actually look like. I am unable to get hold of the torque curve for the motors I have in mind ( This is fine, as the torque curve is stepper specific ... so I have read.

On the X-axis – if I remember correctly, I have a theoretical ratio of 1:10, required v’s available. In practice, when testing the X-axis using an oversized drive pulley and a poorly tensioned section of belt, one side worked really well, the other was satisfactory. As the belt was being held in palce without correct tension this was a good result. A confidence builder! Once the pulleys and belts are in place, I can run a second test, adjust etc and then attach a line and weight to the gantry and let gravity tell me how much force is required to move the gantry, in particular the friction coefficient.

Steppers, after bit more reading, I realised this isn’t the place to start when thinking about building the circuit ) I need to be thinking in terms of ripple, electrical noise, and clean/dirty sides of a circuit.

http://www.mycncuk.com/threads/6696-...machine-wiring

http://www.mycncuk.com/threads/7450-...ical-behaviour

Stripping back on some of the technical detail, I think I need to focus on segregation, shielding, filtering and then follow best practice, as detailed within the document and many of the build logs. I will write something up, best way to avoid mistakes.

As per the second link, it looks like Leadshine is ‘the’ brand and they offer an anti stall feature, which is important feature when slaving motors on such a light rail.

Next steps, take the frame apart and PU the mdf. Order a few non-essential elements, write up the outline for the electrical circuit, order the pulleys and belt.

Quote:

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Originally Posted by Rich

So after further research I found this website:

http://www.orientalmotor.com/support/motor-sizing.html

The numbers offer a guide to the amount of torque required to move at specific feedrates.

The issue now is what will the available torque curve will actually look like. I am unable to get hold of the torque curve for the motors I have in mind ( This is fine, as the torque curve is stepper specific ... so I have read.

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Can I say after reading your initial first post outlining the simple usage of router style machine that your going far too deep into what will in practice make very little difference to how simple router works.

Don't get me wrong there's nothing wrong with learning about the technical side of things but honestly in practice for this type of machine there's not much to decide on the stepper side other than size and drive selection.

In practice what will Make or Break the machine will be YOU and YOUR skills and ATTENTION to DETAIL in how you build the machine rather than if the motor speed curve is optimum.!! . . . Poor build quality can make a perfectly suitable sized motor/drive /psu setup perform like bag of nails.

With typical stepper systems in basicly boils down to if you run on 50Vdc drives or 80Vdc drives. With voltages around 36/44Vdc and 60/70vdc respectively.
If 50Vdc then lower sized <2nm steppers are often used and on smaller size machines.
If 80Vdc then >2nm steppers are used and on Medium to large-ish(4x4) size machines.

Personally I mostly use 3nm motors running at 68Vdc with Digital drives on any size machine larger than A3 upto 4x4 as the money differance between smaller setup is nothing and the performance of this combination covers a large range.
For those with little engineering skills or tools they also offer a safety net to account for less than ideal build and will transfer to the inevitable next build.!!

It's really not rocket science regards steppers and doesn't need to be turned into it for straight forward router style machine. IMO DON'T try to re-invent the wheel just go with a setup what's proven to work.

Thanks Jazz. I hear what you are saying. A bit of research is just a way of ensuring that any good advice I receive is not wasted and I avoid losing too many steps )

The build quality is good. All the holes are drilled accurately, helped by the use of a USB microscope, unfortunately they are not always drilled in the right place.

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Originally Posted by Rich

The build quality is good. All the holes are drilled accurately, helped by the use of a USB microscope, unfortunately they are not always drilled in the right place.

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Ah ah isn't the point of accurecy to be that holes are in the right place. . . :hysterical: . . . No drill makes an accurate hole.!

Per an earlier post, I’d run through ‘Gecko: Step Motor Basics’ and put the details into a spreadsheet, the results reflect the numbers quoted by Jazz. As the basics of building a dedicated PSU have been clearly stated, I will give it a go.

I will follow the PSU circuit provided by Irving, except for the safety circuit, which will be adjusted to include things I already have hanging around:

- NVR Switch, removed from a 240v hobby router table
- Zig CF-8 charging and distribution unit 12v http://www.zig-electronics.co.uk/products.htm#
- 240vac, 25 amp Consumer Unit
- STAC, AC voltage regulator, ST500W (Type D) http://stac-japan.jp/portable/

Zig unit will be used in the safety circuit, in place of the 24vdc transformer. The NVR switch is an option, but more probably a 12v momentary push button switch.

The Consumer Unit can be used as the primary switch (C or D rated MCB). The AC regulator can be wired into the safety circuit, using a third relay. It will take power from the 240v garage supply. I’m assuming I can break into the cable between the mains and the unit, so the unit and the spindle will be isolated when the e-stop button is pressed.

I'm still roughing things out and will need someone to review the completed PSU before I turn it on?

The methods described in your link from Oriental Motors are essentially the same as my script here. Mine is a bit more detailed in some areas, for what it's worth...It's also to get a qualitative feeling for the system.

If you don't have the torque speed curve for a particular stepper motor, a reasonable assumption is that it outputs 2/3rds of the rated holding torque up to the corner speed, then assume constant power from that point. This is essentially the method used in Irving's spreadsheet. This is of course an assumption, so it's safest to design for just below the corner speed, unless you're very confident about what you're doing. I guess I could add a plot of the stepper motor torque speed curve and machine torque requirement to my scrip, then look for the intersection to find the maximum speed... but nobody seems interested.

​Thanks Jonathan, I will run the script and see what I am able to do. Irving's spreadsheet was a good place to start. Although my machine doesn't quite fit the profile the sheet expects, I was able to gain a sense of what factors where critical to the design/specifications of the machine.

Should you do decide to write the additional script, it would be interesting to see the distinction between the projected and real world examples. This is v.1, so knowing the maximum top speed at which the machine is able to provide sufficient torque to cut particular materials would help with v.2. The gear ratio on v.1 is just an informed guess and now the holes are drilled, there's no way back! ​

Quote:

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Originally Posted by Rich

​This is v.1, so knowing the maximum top speed at which the machine is able to provide sufficient torque to cut particular materials would help with v.2. The gear ratio on v.1 is just an informed guess and now the holes are drilled, there's no way back! ​

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The speed/torque of the stepper motors won't be the limiting factor regards cutting speeds.? It will be Spindle power and machine stiffness/build quality.!!

Yes but, no but, yes but, no but, yes but ......... )

And I did include the phrase 'distinction between projected and real world', covering all my bases! You're just being selective.

This might explain better; http://www.mycncuk.com/threads/2148-...2975#post62975 :joker:

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Originally Posted by Rich

You're just being selective.

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No it's called being realistic.!!

Jazz, I get the point. Using a spreadsheet doesn't distract from the issue of build quality. If the error rate between projected and real world is 20% and I've used all the right parts (as detailed clearly within the forum), then the figures will tell me I can't build a thing worth a damn. My issue, the things I need to be realistic about. I haven't used all the right parts, but then I'm a novic and likely to break, bend and drop things. So I design with this in mind. I have two key issue to resolve within this design. The first is to learn everything I can from it, the second it to buy the electronic responsibly so that don't end up dumped in a foreign country. If I do it right, the worst thing that will happen is the aluminium rail with travel 5 miles to the local smelter.

BTW: I've not quite finished reading all your posts )

Could someone please let me know what the answer is here - I just need to have these thing clear in my mind as all the calculations can be a bit confusing!

The PSU based on the following transformer is quoted within the forum (building a PSU is a risky business) :

http://www.airlinktransformers.com/c...nge/CM0625250/

When wiring in parallel, the output is +/-70vdc at 12amps, providing 840 watts. This is just less than double the 430watts, measured while a machine was in motion.

An alternative transformer appears to be:

http://www.airlinktransformers.com/c...nge/CM0500220/

When wired in series, it makes available 700watts (56volts/12.5amps). The figure I have for the motors suggest vmax for the motors at 57 volts (4.2amps,3.2mH).

So why would I build the PSU using the a larger transformer? It affects the number of capacitors required? I'm just running calculation ...

C = 0.1 * A/V for a 5% ripple = 0.1 * 12.5/56 = .022F = 22,000uF with a voltage rating of at least 100V and a ripple rating of 12.5A.

I read somewhere that voltage, in this instance, is like pressure in the system, its re-supplying the motor. I understand there is an issue of impedance, but there are capacitors and back EMF resupplying the circuit. I'm assuming the transformer in continuous use will heat up and so the rate at which is can provide power will slow. Is that the point?

Another point, the BOB (OPPB v.3). Just checking I don't need to worry about its maximum voltage or current unless I am running ancillary items via the BOB. It's not part of the power circuit, its just pulsing the steppers with go/stop signals?

If your drivers can take it go for the higher voltage as this translates directly to upper speed limit. Current requirement is typically 60% of motor rating, so.60% x 3 x 4.2 is 8A approx. This means you can get away with smaller capacitors .1 x 8/70 is approx 12000uF @ 100v, ripple rating can be lower at around 4A.

Re BOB, correct only 5v for signalling and 24v for limit/home switches needed. All i/o should be opto-isolated at the BOB for inputs and at drivers for motion control step/direction or relay outputs for other controls.

Quote:

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Originally Posted by Rich

Could someone please let me know what the answer is here - I just need to have these thing clear in my mind as all the calculations can be a bit confusing!

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I've mentioned the ideal voltage to run these motors at and why in 2 post's now but you seem not be listening.! . . . One more time then with little more WHY.!!

The Gecko site suggestion is working on the safe side but in practice the modern hybrid stepper motors we use and in particular the low inductance 3/4Nm available to us easily handle 70Vdc. Combine this with Modern Digital drives which handle current, motor heating and resonance much more efficiently then performance is greatly increased in several ways. More speed, more torque at higher speeds and smoother running motors.

Regards the transformer then all you really need is to size it so it outputs the voltage required and some extra amps for overhead. The volts are the main thing to concentrate on because if you go to high here you can blow the drives if tolerence peaks higher than there max rating. This is why 80V drives running 68Volts is safe.
You can get away with 500Va and 2x50V wired parallel or 2x25v wired in series with 3 x 4.2a motors without any troubles and I've run these with 4 motors in past without any issues but the 625va is the better option with 4 motors as it gives higher safety margin for say 4th axis.

Reason you can do this because all 4 motors are never pulling full amps at same time and the way the unregulated transformer/drives work they only pull amps on half the PWM cycle so don't draw the full rating of the motor. Combine this together and you can get away with Transformer Amps 60% of total motor amps but you still need the voltage to get the speed/torque from steppers.

Like irving says you can get away with much less caps and using 3 x 4700uf wired in parallel is my prefered way as they are cheaper, easier to find and lower ripple I believe.!

Regards the Bob then not sure what your meaning because voltage is very important to the BOB.? . . Feed it more than it's I/O can handle and you'll fry it every time, infact on the cheaper Bob's like the Oppb v3 you'll drasticly shorten it's life if you run any where near it's limit.

99.9% of BOB's will have voltage requirement or voltage range to operate and run things like Opto's and relays etc. The Motor output side of a Controller is often 5v logic and all the BOB does is pass it thru or in some cases will filter and boost the signal to 5V if lower.
Only the standard I/O side can vary regards voltage/current and even then your BOB will have a limit it can handle. The cheaper BOB's will restrict you to 5V others will be 24 or 30Vdc.
Again in practice your better running 24V thru I/O and the safety system limits Etc to help resist any noise interference.

DONT buy a cheap BOB they are very important and seriously under rated in how they can negatively affect the machine performance and shorten the life expectancy of your Hair.!!

Hope this helps.!

Thanks Irving. I have a parts list together now )

Thanks Jazz, I won't be adding a fourth axis, so the 500va transformer is all I need.

The specs on the BOB haven't changed - OPPB v.3. I have a 12 volt supply to hand, although I may well need to supply 24volts for the alarm circuit, quoted as 30v @ 100mA.

Does anyone have a recommended source for the Leadshine AM882 stepper, someone on Aliexpress perhaps?

Been a while.

The table is finished - top need a final coat of urethane. The internal section of the table was coated with an urethane, grout like in its consistency, and has dampened the vibration. I haven't measured the frequency response - but visually I'm happy. The table was built with three internal vacuum boxes. They work, but I messed up the table top. When it came to the final construction, it tuned out that I'd not thought through or simply measured properly the height of the sections I was using. At the last minute I changed my approach and made matter worse than they need to be. I can fix the residual issue - its just annoying to have to fix the issue.

The table slides over a wooden bench and locks tightly into place. Its bloody heavy and a little clumsy - so a couple of height adjustable wheels are required to make this a little more practical. They will aid the lifting of the table when the front end is moving over the side ramps. Its set up so when table drops into place it meets its mark and all the feet then touch the floor. The addition of the extra weight of the gantry has just made the lifting of the table tricky - no place to grip at the right height for lifting.

Once its over the bench its becomes a solid unit - aided by a couple of clips and jams.

The machine has come together. Everything in place except the leadscrew - just need to get that on a lathe. The belts and pulleys have been fitted - the belt has yet to be bonded into place. Various threaded holes in plate aluminium have been re-enforced with backing nuts. I've yet to add any thread lock. Flange bearing, Thrust bearing and bright bar, all purchased from Technobots: http://www.technobotsonline.com/ - fast delivery! I just need to find a couple of crank handles - just in case I need to back off a motor or two in the future. I have two, but they have the wrong ID.

The parts for the PSU should start arriving tomorrow. I will be following the plans set out within this thread:
http://www.mycncuk.com/threads/5075-...ght=Confirming
A Great thread.

Having one motor to hand, will help with the setting out of the cabling.

Started looking for a motion control cards - this seems to be a fair summary of all the basic points. I suspect it will be the last thing I buy - those 12 months will soon tick by:
http://www.automation.com/pmd/Motion...hineDesign.pdf

Dust extraction is mostly finished - up and over the table, as per the spindle cable.

Can someone let me know if it is normal to blow a fuse in the circumstances?

I am in the middle of the PSU build, per the above thread, page 5. The basic circuit is complete, as shown in the following photographs. The initial test suggested the PSU was working - output 70vdc, so I start to solder a few of the parts together.

Once the basic circuit was complete I tested how the circuit performed with the 24dvc regulated power supply - just arrived, running across the SSR. The test was simply switching it on and then off. At which point, I blew the primary fuse, tripped the primary switch and blew the 13amp fuse in the socket. The primary fuse was a 5 amp spade fuse - as no motors are connected

I've not wired in the Relay 2 NC and I the eagle eyed will notice I've forgotten to wire in a secondary fuse.

Is there an obvious reason for this? Or do I need to provide more detail.

http://www.mycncuk.com/attachment.ph...id=15107&stc=1

http://www.mycncuk.com/attachment.ph...id=15108&stc=1

I think it would be good if you put a schematic up exactly how you have wired it. Is that a RCD on the main fuse? If you have blown the 13A fuse you may have an earth fault. Is there a reason you are using an SCR in the circuit? What type of MCB have you used ie B type etc? ..Clive

As Clive said, a diagram would be best. However I'll risk guessing - if you're connecting the transformer to the mains without a soft start socket, then the inrush current from charging the capacitors may be too high. Also, are those automotive type blade fuses and are they used on the mains or 70V circuit? If so you shouldn't use that type there as they're only rated for 12-24V. To be fair the fuse still seems to have worked... but that's maybe not the point!

I'm not an expert on electrics but I wouldn't use the automotive fuse on mains AC. Either MCB or DIN mounted glass fuse holder designed for AC would be my choice.

I did a lot of looking into fuses for the DC side and concluded that it was ok to use a 5A 12V automotive blade fuse at 5A 70V because the fuse would blow at a certain power which is the current squared times the fuse resistance. The voltage didn't come into it until the fuse blew and the gap created needed to be big enough to prevent an arc ( therefore still allowing current through).

That was where I got to it anyway. I also saw Irving use one ( with a disclaimer)!

Clive - you wrote SCR did you mean SSR as in solid state relay?

Thank you all, I can see I've made a mistake by using a spade as a primary fuse. The intention was to use a slow blow fuse, per the thread. I have one ... but because it wasn't on the purchase list, it dropped off the build list.

I will draw a schematic and add a parts list, that will help clarify my issue and hopefully put me back on track.