3' and 2' arboga
Tom1, power feed and smoother travel are two big differences. The RLM models have ball bearings on the ram travel. Probably other differences, such as motor HP, but the power feed and quicker/easier ram travel are huge improvements that would make the RLM3508 much more desirable to own.
I worked with both the 3' and 2' arboga radial drills. The 3' is comparable to any quality large radial arm drill.
The 2' is the perfect sized radial drill IMHO. Manual vertical and manual horizontal... with enough wheels and levers to keep me happy. Geared head is the way to go... nobody likes changing speeds with belts...Has a large rec. swing-away cast iron table so you can use the floor base a work stand for larger/taller sized metal things that need to be drilled.
I have been looking to buy one ever since. (In fact, if anyone here is selling an ER830 ER825, contact me.)
They would both turn holes in thick plate as big as the goofiest-largest bits we had. ... if you can stuff the bit in the chuck, odds are it will do what is asked of it.
And they both had hand scraped ways, which seemed factory to me.
To this day I have a pretty big crush on the 2' models.
-Drew