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Please help diagnose table saw burning issues

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Forum topic by ihadmail posted 03-11-2017 12:56 AM 413 views 0 times favorited 8 replies Add to Favorites Watch
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ihadmail

61 posts in 354 days


03-11-2017 12:56 AM

EDIT: Issue solved! I missed the spring tensioner when reassembling the saw, which was allowing the belt to slip.

Hi all,

I’ve recently rebuilt a Dewalt 746 table saw that was badly rusted. It does not cut well though. I am getting very bad burning from cross cuts with the miter gauge, cross cuts with the sliding table and rip cuts.

So far I have checked the blade parallel to the miter slot. I used a woodpeckers table saw dial indicator setup. I’ve measured this multiple times both at the tooth and at the blade body and am getting less than 1/2 thousandth difference between the front and rear of the saw.

I have checked the fence square to the blade using the 32nds portion of my combination square rule. It is within much less than 1/64th of being parallel to the blade.

I have checked the fence parallel to the miter slot using the same woodpeckers dial indicator. I am within 1 thousandth measuring the front, middle and rear of the fence.

I have checked arbor runout using the woodpeckers dial indicator. I first measured the face of the flange that sits against the blade near its outer circumference and got less than 1/2 thousandth movement when turning the arbor. I then moved the setup to place the dial indicator on the smooth part of the arbor shaft near the flange. Again I got less than 1/2 thousandth movement.

I considered that the motor may be damaged and not running at full speed. So I bought a photo tachometer. It’s indicating right at 3200 rpm, which is within ~5% of advertised speed for this saw and pretty much spot on for the plate on the motor.

I considered it may be a damaged/dirty blade so I swapped beteween multiple blades I have had good success with on my other saw. They were Freud diablo, Freud industrial, Amana and Dewalt blades. They all resulted in a lot of burning. I was using the highest feed rate I could to prevent bogging the saw down.

My last test was back to back cuts between the problematic 746 and my issue free Dewalt 7491RS using the same piece of 4/4 soft maple and the same blade. Here I made a rip cut using the 746 and my Freud Diablo 50t combination blade. It was very hard to feed and caused a lot of burning. I then moved that blade to my 7491RS and made a perfectly clean cut which was much easier to feed. Next I made a cut on the 746 using my Amana thin kerf 24t rip blade. I could feed slightly faster using this blade but it was still difficult to feed and caused a lot of burning. That Amana blade was then moved to the 7491RS and made an effortless cut with no burning. Along with the burning, it seems I’m getting tear out on the cuts made with the 746 and the cuts from the 7491RS are nearly glue ready.

Here’s a photo showing the difference between the cuts. 746 on left and 7491RS on right.

I am really at a loss here. I feel like I’ve investigated everything that could be causing this. I’m fairly new to woodworking. I do have experience using dial indicators and taking measurements properly, not too many years ago I built high performance engines as a hobby and they required extremely precise tolerances.

Thanks in advance for any help or ideas.


8 replies so far

View patcollins's profile

patcollins

1605 posts in 2705 days


#1 posted 03-11-2017 01:01 AM

Does your arbor have any run-out?

View firefighterontheside's profile

firefighterontheside

16963 posts in 1696 days


#2 posted 03-11-2017 01:03 AM

Belt slipping, pulley slipping?

-- Bill M. "People change, walnut doesn't" by Gene.

View jeffswildwood's profile

jeffswildwood

2575 posts in 1817 days


#3 posted 03-11-2017 01:09 AM

Maybe motor bearings going bad and just shows itself when under a load? I’m guessing here!

-- We all make mistakes, the trick is to fix it in a way that says "I meant to do that".

View ihadmail's profile

ihadmail

61 posts in 354 days


#4 posted 03-11-2017 01:09 AM



Does your arbor have any run-out?

- patcollins

If it does it’s nearly zero or I’m measuring it incorrectly.


Belt slipping, pulley slipping?

- firefighterontheside

It’s a new belt but I can try to check this by locking the blade and turning it by hand. Thanks for the idea.

View TungOil's profile

TungOil

748 posts in 335 days


#5 posted 03-11-2017 01:10 AM

Burning is usually caused by misalignment between the blade and fence, but that usually shows up on just one side of the cut. Your picture shows a more even burn pattern on both sides of the cut and your measurements would indicate that things are well aligned. I suspect it might be bad arbor bearings. Put the indicator against the blade or the blade mount and see if you can push the arbor side to side.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View ihadmail's profile

ihadmail

61 posts in 354 days


#6 posted 03-11-2017 01:15 AM

Problem solved.

The motor wasn’t putting enough pressure on the belt and it was slipping.

It helps a lot when reassembling a tool if every critical piece makes it back in place.

This guy:

Is supposed to be here:

View ihadmail's profile

ihadmail

61 posts in 354 days


#7 posted 03-11-2017 01:17 AM


Burning is usually caused by misalignment between the blade and fence, but that usually shows up on just one side of the cut. Your picture shows a more even burn pattern on both sides of the cut and your measurements would indicate that things are well aligned. I suspect it might be bad arbor bearings. Put the indicator against the blade or the blade mount and see if you can push the arbor side to side.

- TungOil


Maybe motor bearings going bad and just shows itself when under a load? I m guessing here!

- jeffswildwood

Thank you both for the suggestion. I used a new arbor shaft and new bearings. There is a wave washer in the assembly to keep constant pressure on the bearings preventing side to side movement.

View firefighterontheside's profile

firefighterontheside

16963 posts in 1696 days


#8 posted 03-11-2017 01:24 AM

Whoops.

-- Bill M. "People change, walnut doesn't" by Gene.

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