Gordon
I want to add a very helpful tip nobody ever mentions that you can do. Why...because they don't about it.
You can pull out on the key once you have some defined cuts filed to obtain marks on the front slop of the cuts. Grumbach made an impressioning tool with a squeeze trigger handle that had a rod sticking out the front. When squeezed the rod would move out and hit the face of the lock pulling the blank outward while you put turning pressure on the cylinder. Makes huge easy to see marks on the front slope of the cuts no rocking the blank required.
This also would make marks on the lock which is not something that is desirable but it works. Was called The Grumbach Impressioning System. I have 2 of these tools. One is the deluxe chrome version not many people where lucky enough to get and the blue anodized one. I used it for a while but found I could do it without the tool leaving no marks on the lock.
I have to add you DO NOT what to use this pulling out method on wafer locks it will bend the disc wafers rendering the lock inoperable and can also distort the cylinder wafer guides. Even if you replaced the wafers the cylinder can be ruined for the most part, sometimes actually breaking off some pieces.
Grumbach warned about this but morons still used that tool on them and complained that tool (not them) had ruined the lock.

So even without the tool DO NOT be pulling outward on the key when impressioning a disc wafer lock!
Thank me very much no charge for this tip.
Richard