I bought a Portek Ultra ChainMaster (http://www.portek.co.uk/UltraChainmaster_Index.html) chain sharpener in February 2012, but for various reasons a year went by before I got it out of the box, only then to discover I needed a different size grinding wheel than that supplied, and it was November 2013 before I eventually got around to setting it up with the correct size wheel and using it for real.
Since starting to use a chainsaw in 2007, I've sharpened using a round file in a guide from an Oregon chain sharpening kit (http://www.frjonesandson.co.uk/products-page/oregon/sharpening-equipment1/oregon-chain-sharpening-kit/). I guess I'd never been that confident that I was keeping the correct angle with the Oregon guide and I thought something like the Portek would give a better, faster and easier sharpening.
The manual that comes with the Portek is a bit of a laugh as it's been poorly translated into English and gave rise to a bit of head scratching in places. In the end I just worked out how it was supposed to work rather than interpreting the instructions. There's a couple of links at the end of this post for anyone that's interested - I've scanned the manual and put it online. There's also a separate copy of the chart which detailes the grinding wheel size and the angles to use for various chains.
The unit isn't freestanding. It needs to be fastened in place. In my case I bolted to a bit of four-by-two and that goes in the vice on my workbench.
Setting about sharpening my first chain it was good to see the cutting edge of each tooth being ground back to a uniform profile and I could see where I'd got the angle incorrect with previous sharpenings using the Oregon guide. They obviously weren't so bad mind that I'd ever experienced any problems actually using the saw! I did three chains in my first session, disappointed to realise though that the Portek doesn't do the height of the rakers and I'd still have to put each chain back on the bar to do those with my flat file and height guide from the Oregon chain sharpening kit.
A few days later in my second session with the Portek I was looking to restore the edge one of those chains and this is where I started to see the failings of the Portek. The two features which determine how much you grind off each tooth are a chain stop designed to ensure that each tooth is held in the same place on the horizontal bed on which the chain sits, and a depth stop which determines how far the grinding wheel can come down. Setting those finely enough so you only touch the tooth for a quick 'brush-up' isn't that easy as there's too much give/flex/spring in the unit. I reckon regular use of the Portek will see me grinding way more off each tooth than is necessary. As you're likely to take more off each tooth than you might with a handheld file, you probably need to check the height of the rakers more often, which as I've already said, the Portek doesn't do.
After one tooth is sharpened, it's necessary to release the clamp which hold the chain stationary, move the tooth forward, hold it against the chain stop while tightening the clamp, before you bring down the grinding wheel. That sounds simple enough but takes longer than moving to the next tooth when using a hand-held guide.
It then didn't help matters that I snapped the plastic handle on the chain clamp (which really ought to be a metal part), and although there's an assembly drawing in the manual showing an exploded and very detailed list of parts, no spares are in fact available from Portek other than grinding wheels. I can probably fashion a replacement handle from some mouldable plastic that I have if I want to keep using it.
I also wonder whether sharpening a chain with a fast moving grinding wheel affects the 'temper' of the metal and the ability of the tooth to hold an edge. I'd appreciate any comments on this from someone who understands how localised heating of the tooth edge by a grinding wheel might change the characteristics of the metal?
I've already decided that for me the Portek is just too much hassle. I've now settled on a Stihl 2-in-1 EasyFile which is quicker, easier, does the raker height at the same time, and which I'll cover in a separate posting (see http://www.swog.org.uk/forum/viewtopic.php?t=1726). For now, the Portek is sitting almost new and unused in my loft. Watch this space if you think you might like it as I'm likely to give it away to anyone who's prepared to collect it or pay the shipping.
Instruction Manual
http://www.simonfisher.org/miscellaneous/Portek%20Ultra%20ChainMaster%20Chain%20Saw%20Sharpener%20Instruction%20Manual.pdf
Chart showing grinding wheel size and angles
http://www.simonfisher.org/miscellaneous/Portek%20Ultra%20ChainMaster%20Chain%20Saw%20Sharpener%20Grinding%20Table.pdf