Blade Alignment

**Stubchain** · 20th January 2005, 12:25 PM

I am about to take delivery of a new Jet Contracting Saw (cast iron wings), having looked at the one in the shop and a bit of research on the forum I decided it was the one for me given the price range etc. I have also found posts and articles on table saw alignment very interesting, as this is a concern to me. The shop owner and myself checked the one on show and it had a blade to mitre slot run out of about 0.2mm, and within manufacturing specs. He seemed to think this was OK. On further reflection and research I have come up with the following observations and conclusions, not sure if they are right though.

By trade I am a precision optical engineer, I used to manufacture satellite optics and weapon systems components etc. All of the information I have gathered on blade to slot alignment centres around marking the blade, using a dial gauge in some sort of jig in the mitre slot to measure the runout of the blade.

If the runout is only measured on the length of the available blade (approx 200mm), and say it is .25mm, the true blade runout to the whole of the mitre slot length (760mm) is in reality just over 1mm.

It would seem to me that it would be better to measure the runout across the entire mitre slot length, if this could be done to .1mm over the whole mitre slot, something I think is achievable, the runout across the blade width would be less than .025mm. Placing a 1 metre steel rule against the blade is a possible option. I am also assuming that the arbour is running true, or as near as possible.

I take ownership of my saw new week and will try to put this into practice, I would like to hear anybodies opinion on the matter if it is possible.

**ozwinner** · 20th January 2005, 08:32 PM

Its woodwork, not brain surgery!!
I think you need to forget about making optics, and concentrate on making sawdust, whether acurate or not, the idea is to have fun.
If everthing was sooooo accurate, then the sandpaper makers would go out of business.

Al

**Groggy** · 20th January 2005, 09:06 PM

Stubchain, some useful links:

http://www.thewoodshop.20m.com/calibrate_sled1.htm

A review of the TS-Aligner:
http://sawsndust.com/r-tsalignerjr.htm

http://woodworking.homeip.net/wood/T...Tablesaws.html

**bsrlee** · 21st January 2005, 02:36 AM

I tend to be with Ozwinner here - the machine is just not that accurate, and the wood itself will move a bit with changes in humidity. I realize that you are used to precision machines but outside a few specialized industries - like you used to work in - you would be hard pressed to find measuring devices that accurate - indeed I'd be surprised if the mitre gauge slot was that straight end-to-end. If the mitre slot is straight, any alignment error will just result in a tiny increase in the kerf cut by the blade - the one you want to watch for is the mitre gauge head being off from 90 degrees to the slot, which will give you problems when you try to put your project together

)

**Stubchain** · 21st January 2005, 01:42 PM

I understand what you are saying about the accuracy etc, I suppose near enough is going to have to be good enough.

**Grunt** · 21st January 2005, 01:54 PM

Originally Posted by ozwinner

Its woodwork, not brain surgery!!
I think you need to forget about making optics, and concentrate on making sawdust, whether acurate or not, the idea is to have fun.
If everthing was sooooo accurate, then the sandpaper makers would go out of business.

Al

Never trust a man wearing a foil beanie.

**silentC** · 21st January 2005, 01:54 PM

If you are looking for a cliche, I'd recommend 'horses for courses'. It's not really a compromise, just a matter of tolerances. I think your tolerances in a table saw are relatively low compared to precision engineering machinery.

I think the main thing with a table saw is that if there is a slight run out, it is away from the side the fence is on, rather than towards it. The other thing to remember is that the wood is already cut by the time it passes the back of the blade, so a slight difference in distance from the fence is not going to affect the accuracy of your cut. If it is too great, you might get some burning on the cut edge where it rubs on the back of the blade, or you might even get kickback in an extreme case.

**E. maculata** · 21st January 2005, 07:59 PM

Originally Posted by silentC

the main thing with a table saw is that if there is a slight run out, it is away from the side the fence is on, rather than towards it. The other thing to remember is that the wood is already cut by the time it passes the back of the blade, so a slight difference in distance from the fence is not going to affect the accuracy of your cut. If it is too great, you might get some burning on the cut edge where it rubs on the back of the blade, or you might even get kickback in an extreme case.

IMHO this advice is Spot on,
it is actually desirable on large commercial bench type ripping saws, it's called "lead in" without it they tend to jam/heat the blade and suffer from erratic sizing, apart from that you may also like to check arbour flanges for runout(uneven holding of the saw) this is done by those in the know on their commercial machines and I have done the same on my shed saw.

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