Re-Building Suregrave CNC

[PeterC]

Hello All,



I recently picked a Suregrave CNC machine, for free, the catch (as always) was the electronics / control board was completely dead. This machine was built ~2005 so I figured the chances of getting any spare parts were next to none. Luckily the machine itself is in excellent condition and seems to have had very little use.


So the biggest challenges I face to get this machine operational are electronic not mechanical. I decided to invest in a DDCS v3.1 system, and build new control electronics from the ground up. I purchased a controller from an ebay seller in Germany. I can'f fault the service, it arrived today, well packaged and everything included and as described.


I've also purchased four new stepper drivers, 2 * 24v DC power supplies and some DIN terminal blocks. My plan is to to build the new CNC controller electronics just mounted on a sheet of wood for now, until I get a better idea of the wiring and size of cabinet I need.



Can I just say DIN Terminal blocks and boot lace ferrules are a revelation!

Next on the list will be a E.Stop relay circuit anda main contactor that will control power to the Stepper PSU and the VFD for a new spindle (that I'm yet to get).

I've been looking at either a 1.5 or 2.2KW water cooled spindle kits on eBay, unless anyone has any better recommendations?

Anyway I hope to post as much detail as I can - and I'm sure to ask lost of dumb questions,

Peter

[Clive S]

I've been looking at either a 1.5 or 2.2KW water cooled spindle kits on eBay, unless anyone has any better recommendations?

Not sure if you are aware there is a member on this forum that can possibly supply you with the above.

(Dean jazzcnc)

[JAZZCNC]

Before buying a spindle are you sure the gantry and in particular the Z-axis is strong enough because these Suregrave machines were built for engraving not cutting?

Both the 1.5 and 2.2Kw spindles are much heavier and longer than the engraving spindle and DC motor that would have been originally fitted, in particular, the length which will act as a long lever and if I recall the gantry uses a narrow rail system which doesn't offer much support for the Z-axis. If the backplate isn't supported well enough or strong enough or any part of the Z-axis is weak it will cause vibrations at the tool which will result in broken tools and a poor finish. Having a heavy and long spindle will exaggerate and quickly show up a weak Z-axis.

[PeterC]

Hi All

Many thanks for the heads up on the gantry strength.

I’m going to be setting up the cnc on it’s stand over the next few days. I might get a dial indicator setup on it and see just how much flex it has. I’ll also look to see if their is any way to beef up the gantry / z axis if it flexes too much.

The old mount for the dead 240v spindle is only about 20mm high and held onto it by the collar only. I was already thinking I’d have to try and make a new mount somehow as the old spindle seems a weird size and I’d think I’d struggle to find another one the same.

Luckily I have a friend with a milling machine, who likes a challenge and accepts beer tokens!!!

Either way, I do like the idea of using a vfd/spindle setup rather than a regular router. Not so much for the cutting ability, but more for the noise.

I’ve seen some 800w air cooled spindles with fans on the top. YouTube gives mixed messages about these, so i’m not sure which way to go.

My eventual goal is to be able to cut up to 18mm mdf and ply, up to 5mm Perspex and polycarbonate. In an ideal world I’d love to be able to cut 6mm aluminium plate but it’s not the end of the world if this is a step too far.

I will post some photos when I can.

Many thanks

Peter


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[PeterC]

Hello All,

Made good progress today. I built an additional bench to hold the CNC. I had to cut into my outfeed table / workbench but I think it's turned out well. When not in use I can fit a board over part of the CNC so I can use the table saw outfeed, I simply have to lift the board out to expose the whole CNC.



Looking at the strength of the X axis. I agree that the axis looks weak, there is nothing support the linear rail against any deflection. I have had an idea to strengthen it up. I'm going to get a length of 28mm square steel tube. My plan will be to bolt this to the back of the linear rail and tie it back into the gantry supports (which are ironically very well built). I'll have to cut a little bit of the thin black plate away t(but this is just cosmetic) to allow the tube and linear rail to bolt into the supports. In one of the attached photos I'm holding a piece of section to give you an idea. Would like to know what you think?

I didn't get time to look at the spindle, that's for another day!

Thoughts, comments or suggestions always welcome!

Peter

[JAZZCNC]

My honest opinion is that you are wasting your time with this gantry setup if you want to use it for a router as it's just not strong enough and certainly would be wasting your money trying to fit a 1.5 or 2.2kw spindle to it. The Single narrow beam just doesn't offer enough support for the Z-axis, really you need another above the lead screw so it offers support for the Z-axis backplate.

[PeterC]

Hello Folks,

Progress update, I've got the X and Y axis moving, Z axis next!

I did some load / deflection tests and I have to agree with JazzCNC about the stiffness of the axis.
First I wrapped a strap around middle of the X-axis linear rail (with the Z axis out of the way) and applied various loads measured with a luggage scale. I then measured the deflection with a DTI. Secondly, I moved the Z-axis to the middle of the gantry lowered the z-axis to it's lowest position. I tied the strap to the spindle collar and repeated loading and measuring the deflection.
Once I had a base line set of numbers I clamped a piece of box section behind the X linear rail and repeated my test and saw a very noticeable improvement in the stiffness in the Y-direction and twisting forces on the Z-axis. So I think I'm going to add this regardless to beef up the gantry - every little helps!

I have had an idea of how I can add a second support above the lead screw as JazzCNC described but that will take some fabrication - so I'll park this for now.

I'm probably going to go for a little 500w spindle for now as a short term solution. This will hopefully get me cutting something at least!

I'll post some photos and vids when I get the Z- axis operational and wire in a few of the limit/home switches.

Peter

[PeterC]

Hello all,

Just posted my first update video. The core of the electronics are done, still plenty to do!

https://www.youtube.com/watch?v=AMDI7uFNv0U

All thoughts, comments or suggestions gratefully received!

Peter

[Clive S]

Hello all,

Just posted my first update video. The core of the electronics are done, still plenty to do!

https://www.youtube.com/watch?v=AMDI7uFNv0U

All thoughts, comments or suggestions gratefully received!

Peter

You are doing a nice job and excellent vid.

[JAZZCNC]

Word of caution with using 48V with drives rated at 50V, esp the DM542 clones which don't tolerate over-voltage well.

Steppers generate electricity when de-accelerating and will send this back to the drives and PSU so with drives rated at 50V Max and 48V PSU the back EMF can easily exceed and damage the drives.
Also with 48V if your incoming AC electricity fluctuates like most domestic supplies do then you can easily exceed the drive's Max rating as the Output is relative to the Input voltage unless regulated and damage them or at best shorten their life.
Another issue with back EMF is that if your PSU's are the regulated type, which the video doesn't show so can't tell, the back EMF can cause them to shut down to protect themselves which is the last thing you need on a CNC machine so regulated PSU is not recommended. The best type of PSU is an Unregulated one and the best type for CNC is a toroidal supply as it absorbs back-EMF much better.

When sizing PSU you really need to leave a 10% safety margin and with 48V you are too close for comfort so I would advise you to keep the speeds and acceleration down.