The issue with router cut mouldings is simple, when hand routing you tend to move more slowly while the router cutter spindle is tavelling at lets say 20,000 rpm, the cutting edge on a 20mm diameter cutter is travelling at 75 kmh whilst say a cutter of 45mm diameter is cutting at 169kmh (which is why big routers have good variable speed controllers).

Due to this the "micro" scallops taken are hard to see hence the smoother finish. If you hand feed or power feed through the router table then the feed speed needs to be slower but consistent and not so slow as to start burn marks. Spindle moulders use greater diameter blocks with cutters protruding a bit further and consequently the speed of travel increases as does the allowable feed rate.

Just hope I got my math right in the above example, the fact still remains that the greater the diameter of the cutter the faster it travells at a set rpm.

Hope this has not confused the issue any more.

Regards Rob.

Rob Johnson wrote (see)

Just hope I got my math right in the above example, the fact still remains that the greater the diameter of the cutter the faster it travells at a set rpm.

I agree with everything else you said Rob, but surely you meant to say that the greater the diameter of cutter, the slower it travels at a set RPM? Or, maybe you're talking about  the feed-rate  of the timber, not the cutter itself? Sorry.  

 Baz, HSS blades/cutters are indeed much easier to sharpen than TCT. A sharp HSS blade will also give a superior finish to that of a sharp TCT edge.

 That's an interesting point you raise on feeding in to the direction of cutter rotation... I wouldn't advise this on a router table. Ever. It can be done with a hand-held router, if you remove the bulk of the waste first. This is a fairly common operation performed with a spindle moulder though - as long as you have a working feed roller fitted!

Nope! OPJ the spindle speed is set but the distance travelled by the cutting edge is greater than the distance travelled by the centre of the spindle per revolution.

If you were at the north pole and stood 1 metre away from the flag for 24 hours how many miles will you have covered? Then stand somewhere on the equatorial line (make it a nice place,trouble free) for 24 hours how far will you have covered? ( this is rotational distance! before some wise... says "but you are standing still!")

It can be an awkward concept to grasp at first look but it really is a matter of distance travelled in a set time.

Oh and lose HSE bit You know what I think of them , you little  you!

Olly.

I did only mean after the profile had already been cut, it is only a way of removing minor blemishes, & certainly not the way to form the profile.

Baz.

Rob.

Great way of explaining it, i was told the outside tip of the cutter has the fastest travel, which i accepted. But your explanation really brings it home.

Baz.

Olly,

I have heard the comment before that HSS cuts better than TCT.....but I think it is one of those myths accepted too easily without question.

I ran a test years back comparing identical TCT & HSS cutters in the same piece of wood. I found the TCT marginally better initially, and of course, it held its edge over time whilst the HSS cutter didn't. Additionally, HSS cutters often "blue" through over-heating, lose their tempering and become bin-material.

I can't remember which wood I used, and I have heard it said more than once that HSS is better in pine.....but given the "fact", I suggest always questioning it!

Mike 

Mike , the cutting angle on an HSS router bit is more acute so sharper than the TCT one .TCT due to its hardness is relatively brittle so the cutting edge has to be less acute to give strength to the cutting edge.

As the cutting edge is thinner on HSS it gets hotter more readily so more care has to be taken with feed speed and amount cut per pass to prevent blueing and then blunting. Man made materials will dull them too fast to make them useful in that respect.

Ben Plewes wrote (see)

Rob, that makes a lot of sense. I hadn't thought of relative cutting speeds in those terms before. I had assumed that rpm control was more about limiting the effects of centrifugal force. Thanks for the insight!

Thanks Ben, only took notice of it really about 10 tears ago when a cabinetmaker and I witnessed a glazing bar being thrown out of a spindle moulder to finish quivering in the door arrow like! Due to his enquiring mind we worked out that it had travelled at around 90 miles an hour!

We changed the wheels on the feed roller next. 

Thanks Rob......you live and learn!!!!!

I wonder if the quality of the cut that I observed all those years back was somehow due to the much greater weight of the TCT cutter?  I have always felt that the lighter the cutter the more likely it was to chatter. Just another Garnham theory!!

I have two 1/2" long straight HSS cutters, that i had given to me, they are as sharp now as when I started using them ten years ago, (I do not use them on man made timber), and the finish is superb, one thing I do use them a lot for, is as jointers on my table, by setting one half of the fence forward with a strip of worktop edging, on small pieces it is easier than on the planer.

Derek. 

Hi Guys!

Sorry can't join in in the evening i'm at work. still makes good reading the next day. Rob you should be ashamed of your self adding to thread at 6.15am!

Firstly Derek, my router in the router table looks like it did have some sort of micro adjuster before i had to canablise the bace to mount it. I'm quite happy with the car jack though the ajustment is right at the front nice and handy. I just need to mack the ajuster stiffer.

Secondly,What were saying is slow the speed of the feed. I'm going to have to read the part about the cutters again for my new book. Just kidding!

Thirdly as were still on the subject the panels i have made. I have left an 1/8 expansion gap right the way around the panel that is 9'' wide. the grove it gose into is half an inch deep this gives 1/4'' to expand or if it was to contract it would still have 1/4'' to move without falling out. This is pure guess work! put me stait! I suppose  were talking about moisture content before building.

Fourthly,the panels are a nice slip fit  perhaps too nice. i'm bit worried they will move should i;

A,Not worry the door in a house won't move that much the thin layer of varnish will hold in place.

B,Put a shaving of wood behind the panel in the grove cutting off the excess with knife.  (i like that one)

C,Put a small dab of glue in the middle at top and bottom of panel in the grove.

D,Put 6'' nails. sorry small brads in the middle top and bottom of panel in the grove.

Mike wouldn't that restrict the expansion of the rails. even though thay are glued to the styles?

P J

PJ,

With my two piece raised panel set, it states, size to be, panel width, minus the width of the two stiles, plus 10mm. and the panel is a very tight fit when assembled,( I have to cramp up tight to get them in), no glue. As for your, well, six inch nails would do the job, a sliver or a spot of glue just as well, but next time you do it you will not put your biscuits so near to the ends will you. The larger the bit the slower the cutter will run, also the slower the feed speed the better the finish, but not too slow as to burn the timber, only costant use will determine this for you, have fun.

derek.