Why/how did I stuff this up?

[TORB]

Hi Good Peoples,

I decided to build myself a new table saw Cross Cut Sled as per this woodwhisperer video 146 - The Cross-Cut Sled - The Wood Whisperer (http://www.thewoodwhisperer.com/videos/the-cross-cut-sled/)
All was going brilliantly. The base was cut to size, the runners were installed and I had cut the two fences. They were square, flat and true. I partially cut through the base and fitted the fence. (Shown around the 8 minute mark on the video.)

I then checked the accuracy of the work. The fence was so close to 90.00 degrees to the blade it was not worth adjusting. The fence was also 90 degrees to the base of the sled. Bloody hell. I had got it right and so close to perfect it frightened me. :oo:

Time to complete the next step. Drill the extra two holes and properly fix the fence to the base permanently.

:o Loads of four letter words! :doh: The fence is no longer square to the base. Played around with shims and eventually get it almost right (but not as good as previously.) Then I made the first cut. :(( The fence is no longer 90 degrees to the blade. Its so far out of wack it will reach Pluto soon. :~

I am pretty sure the problem had something to do with the final two screw holes and the tightening of the four screws. The question is how do I stop that from happening again? I have puttied up the holes so can redo the back fence but want to get it right this time. Suggestions please.

[Damienol]

My suggestion would be to put the new screws 15mm to the side of the original stuff up, clamp securely and drill a pilot hole before driving the screw in

[TORB]

..... clamp securely and drill a pilot hole before driving the screw in

Thanks, but that's what I did the first time. Could the clamping have thrown it out of wack? If so, how do I stop it happening again?

[Damienol]

For sure. If you dont clamp square then this can push the board out of wack a few mm

[ironik]

I did something similar with my first attempt at getting the fence square on my sled and had trouble with the torque of the drill pulling it just slightly out of square each time I tried to screw it in. Pilot holes, tighter clamps (I was using some cheap quick release things prior and replaced them with f clamps) and using a screw driver to drive the screw instead of my drill seemed to solve it - no movement after I had it all positioned correctly.

I'm wishing I used a harder wood for the rails, I get some slight play in it now.

[derekcohen]

Can you glue first, so as to get the exact position, and then screw once the glue is dry?

Regards from Perth

Derek

[Tahlee]

I had similar problems ... and in the end I got a new piece of Masonite from the hardware shop ... laid it on the sled and butted it against the table saw fence. With that in place I then firmly clamped the sled fence (5 clamps) and installed screws every 75mm.
The trick was to get the sled fence clamped down really tight ... and as mentioned above predrill new holes and check after each screw. I also used the 5 cut method to ensure the settings were OK ... and they were within 0.3mm per meter ... close enough for me.

Regards

Rob

[double.d]

When I made mine I clamped a builders square to the base and then clamped the fence hard up to the square.

[Uncle Al]

What type of timber is the fence made of? If the timber has a coarse grain such as new growth Oregon, your pilot drill could go off centre due to the hard grain, and the screw could also be a bit off centre. Gluing first would seem to be a worthwhile way of ensuring a square result.

Hope you get it sorted.

Alan...

[Cam.H]

ugh yes, cross cut sleds can be a pain. I found this video to be very helpful, very long, but very helpful: https://www.youtube.com/watch?v=UbG-n--LFgQ

I haven't watched the wood whisperers video, but the above video is very thorough so might help with keeping this accurate through the whole process.

[Evanism]

You used the method shown at the 11:00ish mark with new holes, feeler gauge and clamped blocks?

With the videos suggestion, a good set of feeler gauges from the car shop is needed. For the pivot screw, I do use a bigger pre-drilled bugle headed bolt.

Thanks for the reminder, it's time to make a new one. The old is a bit ratty.

I've also found that a sacrificial backer of 9mm MDF is useful. This helps with very small tear out, plus I can take it off and mark it with some common measurements to save time in marking the pieces themselves.

[TORB]

Thanks for all the help suggestions and the sled is now finished.

This is what was done differently the second time.

1. The original fence was 16mm thick. A second bit of hardwood was added and after jointing and dressing, it was now 30mm thick. The thicker fence had way more stability.

2. I used F clamps at each end. They were positioned (parallel) in the same direction as the fence, instead of clamping 90 degrees to the face of the fence. That stopped the clamps having the ability to tilt the 90 degree angle of the face to the base. The clamping pressure was also way less than I would normally use.

3. On the first two holes, I used bigger pilot holes, but also thicker screws. The drill bit was only a tad smaller than the screw. (Checked for squareness to the blade and to the angle to the base. Both purrrrfect.)

4. On the final two screws I used the same screw size and drill bit, but did not go quite as deep as the first two holes.

5. A screwdriver was used to tighten the screws, making sure they were not overly tightened.

Measured again and still bloody purrrrrrrr-fect.:hpydans2:

[Damienol]

Great Result