Is this accurate enough for woodworking?

[Arry]

Ok guys, I have for the first time ever used a dial indicator to assist me in setting up my fence.

I then ripped a piece of pine that was 700mm or 70cm long.

I took various measurements along the width of the piece with my digital calipers and the measurements I got were:

26.30 mm, 26.0mm, 25.90mm and 26.10mm etc

In your own opinion, do you think this is accurate enough for woodworking?

The total variance along the rip cut was approximately 0.4 of a mm, so lets say half a millimeter over 700mm length?

Look forward to your thoughts.

Cheers

Arry

[Damienol]

Was the pine square to start with?

[Arry]

Well, I held one edge against the fence and then made the rip so the rip should be parallel?

[malb]

Well, I held one edge against the fence and then made the rip so the rip should be parallel?

My take on this response is that you took a piece of timber and ripped it holding it against the fence, without ensuring that the reference edge was straight before ripping, and you expect the cut edge to be parallel to the reference edge.

If the reference edge against the fence is not truly straight, the saw will not cut parallel or straight because you will get variable contact with the fence, and hence variable width. If the edge is way off being straight there is also a significant danger of kickback due to the material catching at the outfeed end of the blade, being lifted and thrown back at you.

There are jig designs for trimming a straight edge onto work that lacks a straight edge, such as bowed stock or waney edged boards cut from a tree. These consist of a board with a jointed egde that is wider than the board to be trimmed, with overcentre clamps to lock the non straight board. The combination can then be run through againt the fence to create an edge on the non straight board that is straight and parallel to the fence.

In answer to the original question, a .4mm variation in width relative to a well jointed edge is not great, but could be handled with a couple of light jointer passes. If the reference edge is not well jointed, the error really is meaningless.

[Arry]

yes the edge was straight :-)

[malb]

OK, the next round of dumb questions.

Is the fence straight, square to the table over its entire length and parallel to the blade disc. A lot of fences are extruded ali and and can have a a slight bow or twist, either of which may act like a non straight reference edge.

I know you got the dial indicator to set up the saw, but have you followed the set up procedure fully, set the mitre slots parallel to the blade disc, then alligned the fence to the mitre slot to be parallel to the slot. Are the slots each truly straight and collectively parallel, a slight curve in the slot you are referencing from will throw out the readings on the DI and result in a non perfect setup. Is whatever you are using as a DI mount a neat and consistant sliding fit in the slot? The list goes on and on.

[Arry]

Cheers for the responses guys however I think you are going beyond the scope of my question :p

A few things:

1. Blade is 90 degress to the table and is parallel to the mitre slots.
2. I have aligned the fence to the slots as best as I can at this stage with the dial indicator.
2. I have setup Jarrah runners for the mitre slots and then attached a jointed piece of Jarrah on top of the runners, to which I attached the Dial Indicator.

The Dial indicator was just used to help me set the fence parallel.

Have done everything as best as I can.

Then to truly tell how accurate the cut is ie - setting all of this up is one thing but measuring the cut is the only true way :-)

I took a piece of pine that was 70 cm long and jointed, placed that edge against the fence, then made a rip cut.

I then used my digital calipers to measure the width of the cut at various points, the measurements were as previous mentioned.

So basically from the start of the rip to the end ie over the distance of 70 cm my measurements of the width all fall within .5 mm of each other.

So I was wondering if this is accurate enough for woodworking?

Cheers :)

[malb]

I did say that the reported error was not great (as in not good rather than as in not large) but could be removed with a couple of light jointer passes in my first reply. If it's as good as you can get the saw with what you have available, then I guess you will have to find ways to live with it, like ripping slightly over width with the knowledge that you will need to plane or machine to a finished size.

This would be particularly important for joinery (because there will be other components to visually refer to that make errors stand out), or or where the ripped edge is to be routed at a table or with an edge guide because the fence or guide will try to average the discrepancies in the surface when guiding the bit and will again make the issue obvious.

[pjt]

I would expect a bit better than 0.5mm variation, more like 0.1 to 0.2mm.

The fence doesn't have to be aligned with the blade to achieve a satisfactory cut, my TS setup suggests a fence that is angled to the blade to give a wider gap at the the back of the blade, it's only a small amount, the exact number eludes me for the moment.

If you look at the face of the cut there is evidence left behind which shows where the fence is at, if you have generally only downward sawmarks you will have clearance at the back of the blade, a mix of up/downward means parallel and if only has upward sawmarks the fence will be narrower at the back, this is the least desirable situation. This will be opposite for the offcut except when parallel.

When I set a distance I do it at the front of the blade to the fence and this then is the width I want, I don't want the rising teeth (back of blade) to remove any material and give me a thinner cut piece than I set at the front of the blade.

I would suggest a few more test cuts and after each cut make sure the timber hasn't moved during the cut, (tension release/twist). make flat/square if needs be.

Other things to consider might be rigidity of the fence, maybe there's a bit of variation in how firm you are being in keeping the job on the fence, maybe there's a bit of drift away from the fence, if you look at the sawmarks are there any steps at these differences in width or is it a reasonably smooth face?

Pete

[auscab]

Hi Arry,
A table saw for a lot of the work I do is mostly a roughing out tool ,Thats for the rip cuts I do any way, all the saw marks are removed later,things are always cut over size then planed to fit, when do you see polished saw marks on the edge of furniture ? So you can get away with a bit there.

It would be nice for you to know why it is out .4mm over 700mm though, and get it right or better now while your into it.

The first think I would be doing is seeing how much hand pressure it takes to move your fence .4 of a mm
It could be your sawing technique, and your fence could be flexing a little , every one I have ever used moved with pressure ,and I think the only ones that don't move are fixed at both ends when clamped. Ive never had one of those fences fitted to any of the table saws Ive ever used though.

When setting up my saw, Rather than measuring out off the teeth of my blade to the slot on the table ,I placed a straight edge carefully against my teeth , I helped it stay in place with magnets .

The type with a switch on them, These .

Magswitch® MagJigs : CARBA-TEC (http://www.carbatec.com.au/magswitch-magjigs_c20286)

you could get by without them . and I measured from the steel straight edge to the slot at the front and back of my table , this worked well for me and I got it within .1 and .2 of a mm out at those points, so in at the blade the distance out was a much smaller amount. I think when I did this I worked out the slight run out of the blade and marked two teeth opposite each other that were the the same to work off.

What you really need those slots to be true to the blade is for cross cutting, especially with using cross cutting sleds , they are a very good safe thing to be setting up on a table saw and have lots of uses.

Here is a good demo on one, there are more on youtube if your interested

146 - How to Make a Cross-Cut Sled - YouTube (http://www.youtube.com/watch?v=uE9f4bp_wm8)

Rob

PS , Typing this out the same time as Pete did .

[Arry]

Thanks heaps guys

I am going to go out today and re go over everything to see if I can get a better result.

Cheers for all of the help so far.

Much appreciated.

[Trav]

Your technique can make a big difference too. If you pause or accelerate etc as you are going through the cut it could easily make a 0.5mm difference. Try using a feather board to ensure there is uniform pressure on the timber as it goes through the blade, and keep your feed rate steady.
Plus all the other things others have suggested.

Trav

[MicN]

To me: Calipers aside, are you satisfied with the end results produced in your work? Then it's accurate enough.

If not, then pull out all your measuring gear and keep going until you are. In the end, it's you that's using it and you who has to deal with how it works. No-one else can tell you what you'll be happy with.

[safari]

I second Trav's comment about the feather board. I recently bought one that locks into the mitre slot and found the quality of the cut improved.