Hi all,
I recently got a second hand welding table from Sigmund like this one here
It’s in good shape overall but not new and it’s been transported a couple of times already, so…I’m not quite sure how reliable is for checking alignment.
My question is, what’s the best way to check the flatness across the table? I could check it with a 90x90mm aluminum profile which should be fairly precise but is there any other way?
Thanks!
I wouldn’t use extruded profile unless you had also validated that was flat. A steel straight edge and feeler gauge set is what I used. I have a similar table (Rhino branded version with 16mm top). When I was checking for flatness I found that even though the top is substantial and there is ribbing on the underside, adjusting the feet still made a considerable difference to the flatness. Obviously if yours is used I can’t guarantee the same but I found it pretty easy to get it flat (at least flat enough for framebuilding).
How do you know the steel straight edge is actually straight. I’ve bought one in the past I threw out once i realised it had a curve in it. You need to start with a know flat surface as your reference to calibrate /check the tool you are going to use.
Um, no. A straight edge is perfectly fine, as long as you know to what standard it’s made, and there’s varying levels for that. And straight edges are the standard tool used when creating flat surfaces…
This for example would work fine for this purpose (.084 mm / meter):
se.rs-online.com/web/p/rulers/2545734?gb=s
A700000009424058.pdf (rs-online.com)
If you’re feeling unnecessarily ambitious and want to chase your tail (33 μm per meter):
se.rs-online.com/web/p/rulers/8771797?gb=s
0900766b81408849.pdf (rs-online.com)
Also ask yourself to what tolerance your materials and other tools are made. It’s silly to hunt after tenths of a mm went no frame tube is made to that tolerance of roundness or concentricity and it will have no effect on handling of the bike.
Regarding “certified” stuff, you also need to be wary of where you have this top-level kit. Temperature and placement can make some of that irrelevant.
We’re building bikes, not uranium enrichment centrifuges.
Well I’m lucky to have a certified granite table to check against. The point I was making is that I’d trust a quality straight-edge before I’d trust an extrusion.
Ahhh…see when I read straight edge I immediately thought of say a steel meter rule, not the one linked above. Those above, I would use as a reference for sure. I have a big cast iron reference table that everything I make gets checked against and chasing tenths is staisfying.
Do these kind of “straight edges” need to be stored at certain temps/humidity levels? in particular the 33um ones… I always wondered that.
No, they don’t require special storage other than to prevent rust. The temp issue is in regard to thermal expansion. Holding the 33 um straight edge in your hand for a few minutes would probably be enough to throw it off the tolerance. Richard Sachs once posted about frame alignment with the observation that a frame half in sunlight will measurably change the alignment. Everything needs to be at the same temp.
