How Flat is Flat?

[tophat]

I've just bought a Planer/Thicknesser and in the process of setting it up I placed a engineers straight edge against the cast iron surfaces. The Infeed table was spot on, couldnt get a one thou gauge under it anywhere. But the Outfeed and the Fence weren't. The outfeed table was humped slightly, in that the straight edge rocked by a max of about 10 thou. The fence was cupped along it length, with a gap in the middle of about 15 thou. So i suppose my question is, is this acceptable on a P/T costing £740?

 

[custard]

I seem to recall that the British Standard for the sole of a bench plane costing less than £50 is flat to within +/- 3 thou, I'm not aware of any similar standard for planer/thicknessers, but I'd say that a 15 thou curve on a fence isn't acceptable on a £740 tool.

 

[bugbear]

The outfeed table was humped slightly, in that the straight edge rocked by a max of about 10 thou.

If you want to quantify a hump more accurately, you can do it by using three feeler gauges.

Put two equal feeler gauges slips at the extremes, thick enough that the straight edge doesn't touch the bump. In this case it sounds like 15 thou would be a workable choice.

There should now be a gap between the hump and the straight edge. This can be easily measured in the normal way with a (third!) feeler gauge.

The hump is 15 thou minus whatever feeler gauge fits the gap.

I've measured plane sole convexity this way.

BugBear

 

[9fingers]

Reject it!

This degree of error with be a continual PITA when trying to set the machine up for critical tasks like jointing the edges of boards

Bob

 

[tophat]

Thanks for the replies, I didn't mention it yesterday (because i wasn't sure whether it could be adjusted) but the tables weren't co-planar either! The in feed dipped toward the cutter in relation to out feed by 1mm+. Anyway the upshot is: its going back.

 

[dance]

What make/model was it?

 

[tophat]

Its the axminster AW106PT2 and I've got a new one coming Thursday, they gave it the once over and reckon this ones ok. Will check it myself though before it's unloaded. I emailed axminster about the tolerances the machines were built to. They didn't know, but forwarded my email to the factory. Apparently, as long as the fence is straight to < 0.3mm over 1000mm and the tables are flat to <0.12mm over 1000mm its a goer. Unfortunately they didnt seem to understand 'co-planar', so couldn't provide me with any info along those lines.

 

[kirkpoore1]

I'm not in the habit of making excuses for Asian machines, but is there a chance you might have tightened things down too much during assembly? It's possible there is some deflection. Check the manual so see what possible adjustments there are.

I don't think a lengthwise cup on the fence will have any effect. If the fence is perpendicular to the table, when you're edge jointing you'll still get a square edge. When you're face jointing, you won't care. A little left or right deflection won't matter.

I'd be more concerned about the hump in the table. However, a face jointed surface isn't a final surface. I'd run a few boards over the planer to get a reference face, then run them through the thicknesser, taking some off of both sides, and see what you get. Then let the boards sit for a day or two, and check them again. It's likely they'll move enough to overwhelm any difference in face flatness.

Kirk

 

[tophat]

Hi Kirk

The machine was 90% assembled, all that was required was the fitting of the fence and guard. My measurements were made pretty much straight out of the crate on the tables and the unassembled fence. Hopefully this new machine will be better and i will bear in mind what you have said.

thanks

Chris