Do you trust the rip scale on your BT?

[Knottscott]

I always check with a steel rule.The plastic thingy on the fence can move and you would'nt know.Also changing between saw blades, thin kerf and regular kerf changes the distance. I don't trust any of the scales on the saw.I measure witrh known good scales and angles. I use a ruler as little as I can, I do most cuts by fit and feel. Its just my way of doing things, it works for me.
Wayne

I've got a left tilt hybrid and tend to use thin kerfs, but I always set up my scale to a full kerf blade, then I use a shim from a stacked dado set to offset the thickness difference. Switching to the full kerf takes a matter of seconds now.

[spazlab]

What is a Starret rule ?

Starret makes high precision measuring devices of all types (rules, straightedges, dial indicators, etc)

http://www.starrett.com/

[LCHIEN]

What is a Starret rule ?

Starrett is the Cadillac of the rule making companies.
$179 at HD.

[rickd]

Rick,
I never gave it a thought but my saw is not a BT3. The difference is the way the blades are mounted.. On the BT the blade nut is on the left side of the blade, mine is on the right. My saw is a craftsman, the one they discontinued when they came out with the hibred (zip code ) saws.With a thin blade it moves away from the fence, it wouldnt matter on the BT.
Wayne

hi wayne,

thanks for explaining the difference between the bt3 and some other saws re measurement and thin kerf vs regular kerf. i've actually been wondering about it for a while, but i've been waiting for the topic to come up in discussion for fear of asking a really 'dumb' question . the explanatioon of left-tilt, right-tilt still left me wondering - but the blade nut you mentioned explains it. so, now at least i know what the difference is and why. thanks!

[WEG]

Interesting discussion you got going Loring.
I measure with a rule as well. I have moved my rails on occasion and usually leave them alone until I have to move them again for some other setup. What I would like to see is a "movable" scale you could lock in position once you set it up. But I don't think that's going to happen.
WEG

[JimD]

I use a steel rule to measure the precise position but I find the scale useful for getting close or for non critical cuts. For cuts beyond the length of my 18 inch steel rule, I use a tape measure to check the position.

I also made my pointer on my BT3100 movable. It is a fussy little project but all I did was to make an aluminum bracket that fits into the existing rip fence on the bottom side that I can screw into. I then cut up the stock pointer to make it narrower and add a slot for the adjusting screw to slide in. It works fine but I rarely try to get the position exactly right. I think I can set the rip fence more precisely with a steel rule.

Jim

[vaking]

I took time to calibrate the scale on the rails and now I trust it to the precision of 1/64". Use it all the time. I would certainly trust it more than eyeballing the line on the wood against the teeth of the blade. If I have to go by the mark on the wood, I wood make that line , make a cut deliberately leaving the line intact plus some extra (typically around 1/2") and then make several more cuts gradually approaching to the actual line. A micro-adjuster type approach.
Loring:
You are correct theoretically that there are several thicknesses involved and changing the blade could make a difference but I don't think it is that significant. Let's do some numbers:
Amana full size blade PR1040 has characteristics:
kerf - 0.125"
Plate thickness - 0.105".
That means that carbide teeth extend 0.01" beyond the right edge of a plate.
Freud LU87R010 (thin kerf) has characteristics
Kerf - 0.094"
Plate thickness - 0.071"
That means that carbide teeth extend 0.0115" beyond the right edge of a plate.
If you have calibrated the scale for Amana blade and then replace it for Freud blade you will introduce an error of 0.0015" or about 1/700 of an inch.
I have yet to see a woodworking project that needed such precision. Do you think steel tape or Starret rule will do better?
The worst possible case would be if you replace the standard blade with the blade which has teeth same width as the plate thickness. In this case you are talking about an error of about 1/100 of an inch and blades of this kind are a special type. I believe they are called hollow ground planers. You are not likely to put this kind of a blade by accident.

[LCHIEN]

...
Loring:
You are correct theoretically that there are several thicknesses involved and changing the blade could make a difference but I don't think it is that significant. Let's do some numbers:
Amana full size blade PR1040 has characteristics:
kerf - 0.125"
Plate thickness - 0.105".
That means that carbide teeth extend 0.01" beyond the right edge of a plate.
Freud LU87R010 (thin kerf) has characteristics
Kerf - 0.094"
Plate thickness - 0.071"
That means that carbide teeth extend 0.0115" beyond the right edge of a plate.
If you have calibrated the scale for Amana blade and then replace it for Freud blade you will introduce an error of 0.0015" or about 1/700 of an inch.
I have yet to see a woodworking project that needed such precision. Do you think steel tape or Starret rule will do better?
The worst possible case would be if you replace the standard blade with the blade which has teeth same width as the plate thickness. In this case you are talking about an error of about 1/100 of an inch and blades of this kind are a special type. I believe they are called hollow ground planers. You are not likely to put this kind of a blade by accident.

you're right, Alex, you out-calculated me. I knew the number would be small but I was in a hurry and did not actually run the calculations or make the measurements, I did not expect it to be 1.5 thousands difference, I was thinking more along the lines of possibly a 1/64th or 16 thousandths.
Point well taken.
Obviously a thin kerf vs a thick kerf is in itself insignificant because the reference of off the right edge which is pretty miuch coincident withthe left edge of the arbor spacers for both of them.

[scorrpio]

The real answer to this poll is 'highly depends on what I'm doing'.

If I need to cut a piece that has to 'fit in' with other pieces, I don't trust any scale or rule - I find a way to transfer the dimension itself.

But if I need to cut something to a certain width/length, without needing it to 'fit' anything, I set the fence to the front rail scale without thinking twice.

[mdutch]

Yeah, it depends.

I don't change blades as often as I should, but each time I do, I re-cal the rip scale. For virtually all cabinet work, it's dead on. For small boxes and parts, I get with the rule, or even use a ZCTP and brass set-up blocks against the "fence-side" tooth for very narrow widths.

[GRDavid]

if the spacers on the arbour stay the same, why would the rip scale measurement change? wouldn't the distance from the right edge of the blade, thin or regular, be exactly the same? i only use reg kerf anyway, but i don't see how it should make any difference.

If the saying "Seeing is believing" is true, swap your regular kerf blade with a plywood blade.

[scorrpio]

If by 'plywood blade' you mean one of those all-steel (no carbide) abominations, it should be a non-issue for those of us who never use them.

[ejs1097]

I move the rails too much to use it. Seems like when I think about setting it up I need to make a cut larger then 22" or so and have to move the rails. I'll use it when I get extension rails.

[tojan19]

Don't people think that a little engineering went into the idea of having a scale on the rails? I check the scale daily or if I change a blade or something with a test cut but it's always been the most accurrate for me. Scrap mdf is great for checking the setup. Cheap, flat and square. I just keep using the same board with smaller and smaller widths until it's to small. If the scale is on at one measurement, it will be on at the rest. Adjust it right and it works as designed.

[Raymonator]

Don't people think that a little engineering went into the idea of having a scale on the rails? I check the scale daily or if I change a blade or something with a test cut but it's always been the most accurrate for me. Scrap mdf is great for checking the setup. Cheap, flat and square. I just keep using the same board with smaller and smaller widths until it's to small. If the scale is on at one measurement, it will be on at the rest. Adjust it right and it works as designed.

That's a reply I've been hoping to read. I feel the same way. What use would the scale have if it were not set up to be accurate? I would like to think that Ryobi engineers have put some thought and accurately tested the BT's before putting them on the market. One of the reasons I purchased my BT 3100 was because almost everybody here said they are a great cutting TS and I was repeatedly informed that if I fine tuned it at set-up, it would be a very accurate TS for the money. I'm hoping to be able to rely on the fence once I set the TS up, which will be soon hopefully. Great thread.