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I'm doing some upgrades including some reducting.

The back of my tablesaw has a 2 1/2" pipe on it.

Will I get better collection from a shop vac designed for 2 1/2" pipe, or from a 4" or greater pipe reduced at the tool to 2 1/2"?

First thought is that obviously the bigger the better, but...I know there's more to it than just pipe size, in how ducts and airflow are related etc., so a 4+" pipe to a 2 1/2" could possibly be counterproductive, I don't know...

Whatcha think?

Too many years out of college to do the calculations, but the bigger the better. Also, the shorter the better. But I noticed with my shop vac that it gets clogged up pretty fast and the flow reduces. So perhaps more important is to make sure the filter is reasonably clean. Take it outside to clean it and wear a mask while cleaning.

Bigger is better for dust collector, Ed. They have a lower velocity of air movement, but are move powerful, and can move more material, so if you use a smaller dust port, it restricts have the air movement. Shopvacs have a higher velocity, but are less powerful, and need to maintain that velocity with a smaller opening, so you should stick with the 2 1/2" hose with the shopvac. If you want to hook up the saw to a dust collector definitly go to a 4" opening. Hope I made some sense!

Alex

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"Indecision is the key to flexibility" .... Bumper sticker

Any conversion would happen at the tool.

Specifically...

I'll be ducting in my tablesaw. It will be 4" or more on the bottom chute. I would like to split the line into two 4", one for the bottom and one stepped down to the 2 1/2" connector on the back of the tablesaw, but I'm not sure if the step down will be counterproductive.

I'm inclined to just do it that way, especially as it means only having to turn on one collector instead of two...

So the saw will have two collector attachments?

If so and your main line is 4" I'd keep it at 4" through your wye and step down right at the machine with a 2 1/2"-4" adaptor and a short length of 4" flex tubing.

I had my shop piped at 4" from an older collector and got a bigger one with a 5" inlet but left the piping at 4" because I was too lazy to change it all. Finally I re-ducted to 5" overall following a custom plan Oneida sent me. The difference of 1" was nothing short of amazing. They recommended all step downs be done as close to the machine as possible and minimize the amount of flexible tubing used.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Yup, two ports. One from the back of the saw, and one to collect from underneath.

I plan to wye it right at the machine, likely from 5" ducting, possibly larger...

Ideal would be a 5" or 6" duct to a 5" or 6" x 4" x 2 1/2" wye at the saw. I use big box store HVAC fittings, pop rivets and metal tape to make wyes like that for cheap.

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Steve Smith
"Music is what feelings sound like"

Thanks...