Hi Phil
That is probably one of the smallest spindles I've ever seen! The smallest diameter spindles normally available on kit in the UK were generally 3/4in, but that one looks like 16mm, or possibly 15mm. That may be an issue in upgrading it to use conventional blocks.
Before upgrading there a few things to look at. Firstly are there any cracks in the spindle itself? On French heads these can propagate out from the square corners of the cutter slot. Are there any burrs around the slot opening itself? If there are these will need to be carefully removed by a spot of hand filing or better re-turning the spindle on a lathe. Thirdly how good is the thread inside the top of the spindle. As it's Kity it will be metric, but what size is it? Looks like M8 to me (you said M6), so screw a machine screw into the threaded hole and see if the thread is sloppy. If it is I'd say it is dangerous to continue. What height of spindle to you have? To accommodate a Euro block you'll need at least 45mm of spindle height - 5mm for the shoulder at the bottom of a top hat bushing and 40mm for the cutter itself. Is the available shaft above the table long enough? Finally the opening in the table appears to be around 62mm in diameter. Are there any removeable rings to enlarge the opening? With spindle moulders it is normal to be able to wind the cutter down so that the block sits partly below the table - for cuts such as rebates, etc. Unfortunately the smallest Euro profile blocka available are all around 75 to 85mm in diameter so if you can't lift out another table ring it will not be possible to use a Euro block without starting to build false table surfaces, etc.
Assuming that everything is OK, I'd go for the smallest diameter cutterblock I could find. An ally block might be preferable to a steel one because the steel blocks are very heavy, but both Freud and
CMT do 78mm diameter Euro safety blocks but I think they're steel blocks. The block will need to sit on a deep top hat bushing with a 2 to 5mm thick shoulder at the bottom. This bushing should extend 30mm up the inside bore of the cutter and the cutterblock would then need to be held down using a steel washer sitting inside the recess at the top of the block. The recess on Whitehill Euro blocks is 40mm in diameter and the "washer" supplied with is about 8mm thick, although they are normally used with an M12 or M16 countersunk head hex recess (or Torx recess) machine screws so maybe yours would be best fixed with a high tensile bolt and a thin washer on top:
The only other questions might be whether or not your fence opening will accommodate the bigger block and whether or not you have sufficient rise and fall on the shaft to make the best use of the block
If you do manage to convert this machine I'd suggest checking the state of the threads and inner shaft frequently as I feel you are running near the engineering limits for such a small shaft, although I am erring on the side off caution.
Scrit
