Tablesaw Crosscut Sled problems

[wizer]

Right so I've been in the workshop last couple of days. I'm not 100% but I'm going out of my mind reading about woodworking day in day out.

So I thought I'd make a couple of crosscut sleds for an upcoming jewellery box project. Obviously no one will be shocked when I say that the first one hasn't come out too well. :roll: Now, I should start by saying I recently acquired a very posh shooting board which means this is all academic. But I'd still like to know what's gawn wrong.

Here is a pic of what I was building:

..and this was the process:

1. Planed a piece of Iroko til it was a snug sliding fit in the mitre slot. Then ripped it down in strips of roughly 6mm so that it was just beneath flush in the slot.
2. Square up the 12mm MDF board to 600x600mm. **I find at this early point that my TS is not setup very well and It's not making square boards. I nearly stopped here but I reasoned that the edges of the board didn't need to be square for this.
3. Planed up a 2x4 and fixed it to the base board square to one edge.
4. Scratched my head wondering how the hell I was going to make the runners square to the fence (remembering that the back edge of the MDF base was not square to the edge that the fence was squared to.
5. I Decided to fix one end with a screw and then use a combination square to set the other end the same distance from the edge as the other end. (does that make sense?) Then drive some more screws to secure.
6. Use double stick tape on the other runner, slide it in under the base board with the other runner in place. Lift it so that it stuck in place. Then secure with screws.
7. Fix the back fence flush with the back of the board (assuming no need to make it square to anything).
8. Square the blade with the wixey thing and then make a through cut with the sled.
9. Make a test cut with a board and check with an engineers square.

(sounds quick when you read it like that, still took 5hours over 2 days tho :shock: )

The cut was off by about a degree or two. Not much, but it would have been nice to get it nearer to reduce work on the shute. I was un prepared and only decided to make it when I got in the workshop yesterday, so wasn't following a plan or copying someone elses design. "He's makin' it up as 'e goes along!"

So any ideas what went wrong?

Oh and please. no safety lectures. I intend to fix a perspex guard over the top and a block of wood at the back to cover the blade as it goes through when it's finished.

 

[Mr Ed]

Why not use your sliding table?

I think the one on the Kity 419 is excellent - accurate and when its in the way just slide it off the end of the rail.

Ed

 

[wizer]

No room in my workshop Ed. Not even at a squeeze. I've removed it and it's in the loft.

 

[OLD]

The cut is 2 degrees out of square so move the 'fence' to correct it then reposition the front 'fence' parallel and check that.
What went wrong - is the blade parallel with the groove in the table a pencil line is difficult to get perfect accuracy so temp fix fences and adjust.

 

[wizer]

(homer) I glued the fence :roll:

But I see what you mean. Maybe I should re-make it and have the fence adjustable. The only problem with that is one of the benefits is having that clean kerf line as a marker.

 

[Digit]

When I made mine Tom I started by getting the blade parallel to the slot, after that it was simple, all that was necessary was to fix the stop at right angles to the blade using a roofing square.

Roy.

 

[wizer]

yes I need to spend some time getting the saw set up properly. But how did you square the fence to the blade? Did you make a plunge cut through the board?

 

[OPJ]

Tom, could it have been when you secured the fence in place with the screws? If they had countersunk heads and you drove them in before the glue went off, there's a chance the fence may have shifted slightly as the heads bite in to the recesses.

That's certainly something I've experienced, in the past. Now, I try to clamp it in place with a fast-setting PVA and then drive the screws in after 10-15 minutes, for extra security, really.

Could you lay strips of masking tape on to the face to shim it back?

 

[Digit]

When you say fence Tom do you mean the front piece that the timber to be cut rests against?

Roy.

 

[Steve Maskery]

Tom
Well there is always the old adage "If you can't make it accurate, make it adjustable...". Not much help now, I know.

You have identified a very real problem in this, in that the edge to which the fence must be square, i.e. the runner, is on the opposite face of the baseboard to the fence and is therefore inaccessible.

On way round this is to make the edge of the baseboard truly parallel to the runner, and then you can square the fence to this. One way to do this is to fix the runner to the baseboard, then tun it through 180 deg, so that the saw cuts the edge of the board off. Then that edge is also true and can be used as a ref. Obviously it fixes the size of your baseboard, so if this method makes te base too narrow, consider truing up the ed by running a router against the runner. The ffect will be the same and you have more control over the finished size.

HTH
Steve

 

[wizer]

Olly, I glued the fence on and clamped it, the came back the next day to drive the screws. It's square to the edge of the base, but not square to the blade.

When you say fence Tom do you mean the front piece that the timber to be cut rests against?

Yep, tho I'd call it the back. It's this that needs to be square to the blade. The opposite block of wood is just there to keep the sled together.

I couldn't work out how to make the fence square to the blade or the runners as they are on the other side. But I guess I could fix the runners, then clamp the sled to the table and raise the blade through the base. Then the fence could be fixed square to the blade and then a through cut made.

Sound right?

 

[jasonB]

Just use a bit of 25x25 par hardwood as a false fence then can be tweaked to get the right position, only saw part way through until its right and then you can raise the blade if needed. it's possibel your "bit of 4x2" moved as you but most of teh way through it

Not sure how I made mine, think I used the rip fence to get a parallel slot, then fixed the front fence square to that and laid the strips into the grooves and located them from above. I only use the sledge for mitred boxes and small mouldings, rest oif the time the sliding table is better.

Jason

 

[9fingers]

Tom,

You will find the the ONLY parameter that is important to square cutting is that the table slot and the blade are totally parallel.

This might seem counter intuitive but it is true.

If you want proof, set the slot parallel and your mitre gauge a couple of degrees off 90. Push a test piece through the saw holding the stock firmly in the mitre gauge and you will find that it has cut 90 despite the setting on the gauge.

Somewhere on the forum is a write up of this effect by Paul Chapman and he demonstrated it at a bash last year.

It really is true! honest! it is the axis of motion of the workpiece that defines the angle of cut.

So your sled is not that critical. The saw set up is VITAL to 90 degree cutting.

Bob

 

[Digit]

Right Tom. The base is fitted with the runners and slides back and forth. With the front stop/fence not fitted run the sled into the blade and stop the cut just before it breaks out at the front.
Using a known accurate square place it against the blade making sure that the blade is running true and that the square is either missing the teeth or resting on teeth at the front and the back, glue the stop into place against the square.
Go and have a cup of coffee then come back and screw it into place!
If you don't like squaring to the blade square to the edge of the kerf instead. Use a weight to hold the stop/fence in place till the glue dries.
One point where I might differ with Olly, is if he uses counter sunk screws that is. When drilling counter sinks it is no unkown for the the counter sink to be off centre to the drilled hole, therefore I use round head screws to prevent any chance of the screw head trying to move the timber.

Roy.

 

[Digit]

Though many won't believe it what Bob says it is quite correct. The only reason for squaring up with a sled is to keep the base kerf as narrow as possible to help prevent a ragged edge to what you cut. When making a sled if you square to the kerf in the sled the blade can be miles out of square and still do the job. Albeit with a wider kerf than is necessary.

Roy.

 

[barkwindjammer]

old credit card, shim, test, shim, test, shim, test, dont screw or glue anything down til its right, I think I'm learning :idea:

 

[ondablade]

At the most basic level i've always figured that the fence needs to be squared to the line of the mitre slots - in that even if the blade is a bit off line that'll (the line of the slots) still be the line it cuts.

I've never made a sled as i've always had a sliding table, but the same applies when getting the cross cut fence lined up with the line of movement of the sliding table.

The blade then needs to be aligned with this or the slots to give a clean, square cut. If it's skidding a little it'll drag the rear on the sides of the cut which raises risks like bad finish and kickback, and if bad may knock the cut a bit out of the vertical (due to the blade circle) The cut will as above still be in the line of the slots though.

Some other thoughts:

The pic is probably not scale, but it'd probably be advisable to leave a lot more material to bridge over the saw cut in the fence. i.e. use a deeper piece. Some seem to use a second cross piece or doubler/extension at the rear which means it's possible to complete most cuts without the blade emerging and reduces the risk of injury.

For sure screws and indeed drilling can displace pieces unless they are accurately drilled and well secured. Another way is if the clearance hole in the piece being fastened down is slack or not accurately centred with the pilot hole - this is one advantage of a stepped drill.

Is the Wixey reliable? Does it give the same result measuring from both sides?

The saw cut is the line to square the fence to, but you could probably also align the cross cut fence using a good T square laid against one of the rails - but you might need a parallel spacer to bridge to the cross cut fence.

Checking from both sides if using a square to ensure it's accurate...

ian

 

[Digit]

Ian. The way I normally explain this is this way. You have your sled, now the blade is turned 90 degrees to the slot.
The result is a 10 inch wide kerf and a 5 inch rad on the sawn edge.
The angle of the cut is not in any way altered. If the sled was cutting square previously the cut will still be square!

Roy.

 

[jasonB]

9 fingers and Digit I think Toms problem is that the fence (front part) is not 90 deg to the blade eg the work is being held at 88deg not 90. So the relation of the fence to the slots is the issue as this WILL affect the cut

Jason

 

[Karl]

Tom

Here's my sled

A pic of the underside

The fence is held in place with 3 bolts running into T-nuts embedded in the underside of the base. The holes through which the bolts go are oversized, to allow for squaring up the fence to the blade.

Only took an hour to build, and gives very accurate cross cuts. It can handle sheets upto 4'x2'.

Cheers

Karl