I have seen some drum roasters have the ability to vary the drum rotation speed and I can understand what no or very slow rotation would do to the roast however what are the changes seen in varying from the standard?
Is there more liklehood of tipping etc with a slower speed? Less liklehood of even roasring with a faster speed?

Based on the size of the drum, the rotation speed should give the beans a good mixing with enough contact with each other and the drum, the heat transfer happens with drum to bean contact
Also veins in the drum help and control tumbling, mixing, and contact

So the answer is yes to a slower or faster speeds as long as the above is observed

KK

+1

What "standard"?....there is what works best for any given brand / model machine in fixed speed roasters, and then in machines where you can vary the speed according to your own whim, then you might vary it while trying to keep everything else "fixed", so that you can determine where you as an individual roaster think it works best for you in any partoicular situation. And then if you change some other parameter, that speed may need to change.......

That essentially is the "difficulty" in modern machines with variable parameters. It takes the operator to another level of understanding in roasting in toto and it gets ever more technical as you progress, (if you continue the journey), to give you better results, if you (the operator) are able to discern them (the results).....

And of course, you would be waiting an aweful long time for anyone with any experience in the matter, to take the discussion much further than that ( and give important, invaluable expertise away for nix )

This is the stuff of the real roasting apprenticeship.

I guess a manufacturer would come to a "standard" speed for their fixed speed roasters by way of extensive R & D.

In terms of a variable speed roasters, any particular drum  speed will also depend on whether they also have a variable speed fan and variable burner (or not), because there will be any number of combinations of drum speed VS air speed VS drum temp., and that is where the challenge lies for the operator.  A manufacturer may not (?) necessarily be able to recommend any particular drum speed, because  it may be that there will be different burners specified for different markets as well as any number of other variables, which means there will be different behaviours displayed in any individual set up in toto (which is certainly the case with latest technology professional equipment where there are no "default" settings to start with). 

It may well be, that's its not terribly helpful for manufacturers of small end roasting machines to give newcomers to coffee roasting too many variables to get themselves confused with, and I would rather see such roasting machines produced with no variable burners, drums or air speeds a la "old style" drum batch roasters....but it depends on how you want to look at it  In terms of small end roasting machines produced by manufacturers who themselves seem to be newcomers to this industry, it almost seems like a cop out to produce equipment where they can say to their clients......"we made it for you....now you work it out to suit what works best for you....."?  Seems like a way of getting out of having to sort out the equipment and selling it as fit for purpose straight up to the type of market that the equipment is most probably pitched at (probably beginner level).

But of course that is just one opinion.