@dc42
I have solved the problem. It turned out not to be a faulty board, it was geometry. My mount was designed to be able to easily change hotends. Basically I had originally intended to use a MK10 hotend but later changed it for a V6. I should have made a change to the way the adapter plate was mounted but didnt, long and short was that if the hotend touched the surface at all it had a tendency for the mount to flex slightly and turn into a self-energising brake as the flex decreased the clearance causing it to jam against the surface. I checked the z axis reading on the web control before pulling the plug and saw it was still showing 0.6mm which eliminated the possibility of the bed moving unless it was a very subtle stealth bug. After recovering from the last crash i moved the head back to the same position *power off( and moved it forward and bingo insta jam. That explains why it only happened sometimes, if the travel was in the other direction it wouldnt jam as any flex would increase clearance.

I am currently baking a large humble pie : (

I would have had it sorted yesterday but we had a series of electrical storms and the power kept glitching so no printing or computer.

Sorry for all the hassle, but I had actually eliminated all the possibilities I could think of and since I knew there were no problems with the printer motor/movement/wiring wise it seemed a faulty board was the only remaining cause - obviously I was wrong.

Again sorry.

@danal
Looks like a fun movie! I was actually referring to the fact the Catholic demonic exorcism ritual involves those items!
If you liked the original Evil Dead movie check out the brilliant Ash VS Evil Dead series. Same humor, horror and gore same Bruce campbell oh and as a bonus Lucy Lawless as well.

@patakopecek I sorted out the connection problem and I have only used baby stepping once. It was entirely the problem of the mount. I have already made several perfect prints. Now I am able to fine tune the machine the quality is incredible with no ripples or artifacts -all surfaces are like glass!

Thanks for the tip! I will take a look at that.

So I guess you mean the following:
Create the text, generate the gcode and then manually put in the z axis commands to raise and lower the cutter?

I have a large heavy duty 3D printer with a Duet wifi controller. I want to use it to engrave text into aluminium. I have a 480 watt motor which I am going to attach to the frame and then attach a flexible shaft between it and where the hot end is now. The text is going to be fairly small and I have some 0.4mm cutting/engraving bits.
What software do I need to convert text into GCode to send to the printer? I have searched but everything seems to be aimed at laser engraving.

I have an FlSun as well, really impressive quality prints!
I would just build a copy of the FlSun frame and use the electronics etc from the anycubic. Aliexpress is a good source for all the parts except the alu extrusions and linear guides (never by chinese linear rails/guides). If you are in europe I recommend this company for extrusions, they are beautiful (German) quality and cheap https://www.motedis.de
If you go for linear rails I recommend these guys http://www.chieftek.com in europe they are here http://www.cpc-europa.de/en/contact.html and USA https://www.motionusa.com/cpc-|-chieftek-precision
They are fantastic quality and much cheaper than HiWin.
Good luck and have fun!

Just a thought, but I wonder if rubber vibration insulators (basically a piece of hard rubber with 2 bolts moulded in top and bottom) would work? There are small ones holding a plastic cover to the top of the engine in my car. They can take lots of heat and are moulded so they should be exactly the same size. Something like this:
https://www.ebay.co.uk/itm/Aeromotive-Fuel-Pump-Vibration-Dampener-Mounting-Kit-11601/362096382511?epid=1168728755&hash=item544ea0522f:g:zkIAAOSwWaRZsnyp:rk:3:pf:0
but cheaper!

@wilriker Thanks for the tips!
I didnt actually know I was using absolute extrusion! I have not seen any setting in Slic3r to select absolute/relative extrusion and this is the first time I have really edited a gcode file.
Ok, I have just checked on slic3r and found it (I think) under printer settings>general>advanced>use relative E distances When I hover over it I get a message saying "most firmware uses absolute value" I will give it a try on my next small print and see what happens!

@dc42 Thanks, I will check it out.

@jacotheron Thanks for the information, it will save me a lot of grief! I knew you could change filament but I didnt know I could redo the homing, I thought issuing any commands would make it lose track of what it was doing. that really useful, thanks!

@aidar Thanks a load! It worked perfectly! Thats a lot of expensive filament saved.

Ha! Of course, the the extruder value is constantly incrementing as the print progresses and as I just started the file part way through it would just sit there until it had extruded filament equal to the total for the first part of the print. That was really stupid of me! Ok, I will give it a try.