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By Simon_M
#1288662
I have seen youtube videos for larger platters and have been experimenting with larger workpieces up to 25" diameter.

What sort of woodturning tool is used to get a good flat finish? I have seen mention of a negative rake scraper but I don't have one.

I have experimented with a pull cut with a bowl gouge, a smaller round nosed scraper and the edge of a skew - they are probably all too small, but all that was to hand.

When the work is balanced, what speed can be used, I use 6000/diameter or 9000/inches in inches as a guide e.g. 250-400 rpm?
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By CHJ
#1288667
Simon_M wrote:When the work is balanced, what speed can be used, I use 6000/diameter or 9000/inches in inches as a guide e.g. 250-400 rpm?
There is a speed guide chart in the Help Sticky that is based on a recommended cutting edge speed for most readily encountered woods.

But it is only a guide in as much as it serves to show what should result in optimum stock removal and be safe on sound wood, it also hints at what can be expected on the danger front with anything that is not sound, correctly mounted or subject to operator tool misuse if you are tempted to turn everything at high speed.

Turning time experience paying careful attention to any sound changes, tool chatter, stock fixing security as you go etc. I find is the best guide to personal safety.

Regarding larger diameter on items such as platters, I think it's more about the rigidity of the tooling with longer handles than the actual size of the cutter edge to counter the potential leverage imparted by the workpiece should you get a catch or take too enthusiastic a cut.
By Simon_M
#1288744
I did try three bowl gouges - two have longer handles, two are same width and the results were all about the same. I should have mentioned that this is a segmented ring so the direction of the grain is closer to around than across like a bowl and there is some air gap at the peripheral edge initially. I used a much lower speed to turn this away, but I was aiming for a finish that's straight across.

I did get the result I was looking for but it wasn't as easy as I expected. I suppose I assumed, same cutting speed, same tool = same result without considering that the direction of the grain is changing slightly every 30 degrees. I wouldn't normally power sand, but my bowl sander is quite small, so I used a random orbit sander with an ultra low lathe speed ~50 rpm which seemed to work well. I also sanded with the lathe off and hand turning it because I wanted to avoid the feeling of contours and I'm using ash - seemed to work well.

There seems to be a plethora of videos turning at higher speeds - they only show it when it works and ignore what could happen if it goes wrong - so good luck to them, but I won't be trying it. Thanks for the table, it indicated 250 rpm but initially it doesn't hurt to go much slower.
By Chris152
#1288763
When turning wide, flat rims for bowls (not as wide as you're doing) I've turned to as flat and level as I can with a push stroke starting at the rim and moving toward centre, then finish levelling with a ROS, as you say (if I've understood). When sanding, the bowl rotates at less than 60 rpm, and it creates a perfectly flat surface. I've been trying to avoid using a scraper as I find it creates tearout, but that's probably just my lack of skill.