I have a DeWalt DC390 18v cordless circular saw. This takes 165mm
diameter blades on a 20mm arbour. I can't find any blade finer than
30 tooth to fit this saw. I have seen a Trend 48 tooth blade that has
the same size arbour (20mm) but is 160mm diameter (5mm less).

I have 2 questions. The first of course is if I fit the smaller Trend
blade, will it be dangerous? Secondly, will it give me the fine cut
that the blade is designed for?

Whilst on this subject, am I right in thinking that the smaller the
blade diameter, the fewer teeth are needed for finer cuts? For example,
the trend described above has 48 teeth around its circumference. This
gives 0.095 teeth per centimetre of circumference. On a 300 mm diameter
blade, to get 0.095 teeth per cm you would need 90 teeth around the
circumference. Which is a "fine" or even "extra fine" cut if
you read the adverts. Is this sort of conversion the right thing to do?

wrote in message
ups.com...
I have a DeWalt DC390 18v cordless circular saw. This takes 165mm
diameter blades on a 20mm arbour. I can't find any blade finer than
30 tooth to fit this saw. I have seen a Trend 48 tooth blade that has
the same size arbour (20mm) but is 160mm diameter (5mm less).

I have 2 questions. The first of course is if I fit the smaller Trend
blade, will it be dangerous? Secondly, will it give me the fine cut
that the blade is designed for?

Whilst on this subject, am I right in thinking that the smaller the
blade diameter, the fewer teeth are needed for finer cuts? For example,
the trend described above has 48 teeth around its circumference. This
gives 0.095 teeth per centimetre of circumference. On a 300 mm diameter
blade, to get 0.095 teeth per cm you would need 90 teeth around the
circumference. Which is a "fine" or even "extra fine" cut if
you read the adverts. Is this sort of conversion the right thing to do?


No problem fitting a smaller blade to a saw. It is done all the time. The
only real potential difficulty may be if you are cutting something that is
at the depth limit of the exposed saw blade.

As for a number of teet to smoothness relationship, Like any relationship,
it depends. I am no expert, but for the sawing I do, it probably is true.
But there are a bazillion different saw blades out there now with many
different design philosophies.

I think it really boils down to if you are comfortable with a particulat
manufacturer and saw blade. Find something that you like. If in doubt, cut
some scrap and see.

Another big factor is durability. I have purchases many steel blades for
fine cutting on a job basis. It only has to last one job. And if there is
much cutting, I may get two or more "one job" blades. It was quick and fast.

But other blades I buy I want more durability and the ability to resharpen.

So the great qualifier, it depends.

wrote in message
ups.com...
I have a DeWalt DC390 18v cordless circular saw. This takes 165mm
diameter blades on a 20mm arbour. I can't find any blade finer than
30 tooth to fit this saw. I have seen a Trend 48 tooth blade that has
the same size arbour (20mm) but is 160mm diameter (5mm less).

I have 2 questions. The first of course is if I fit the smaller Trend
blade, will it be dangerous? Secondly, will it give me the fine cut
that the blade is designed for?

No. It will not be dangerous except for the fact that the blade guard may
not cover the teeth on the upper side of the saw.

Whilst on this subject, am I right in thinking that the smaller the
blade diameter, the fewer teeth are needed for finer cuts?

No. That is not correct thinking. You can simulate more teeth by feeding
the saw slower. In addition to fewer teeth you will also have a slower
tooth tip speed because of the smaller diameter and this will compound the
problem. Feed slower to help off set this effect. More teeth tend to make
finer cuts because each tooth takes a smaller bite out of the wood. If you
slow down the tip speed the teeth will tend to take bigger bites and
typically will give you a rougher cut.

For example,
the trend described above has 48 teeth around its circumference. This
gives 0.095 teeth per centimetre of circumference. On a 300 mm diameter
blade, to get 0.095 teeth per cm you would need 90 teeth around the
circumference. Which is a "fine" or even "extra fine" cut if
you read the adverts. Is this sort of conversion the right thing to do?