How accurate should a jointer fence be?

[nblong]

The basic question is how much cupping and bowing in a jointer fence is an acceptable amount?:icon_scra

Being basically a newbie I'm collecting what tools I can afford (and will fit in my one-car garage). Jet's 8" jointer/planer was too good to pass up. The price ($299.99) was right and it got almost uniformly good reviews from Amazon. I'm not planning on using it for anything large (small things like jewelry or music boxes mostly) so I don't care that the infeed table is too short to joint an 8' board. However, during setup I discovered the fence is cupped and bowed. I have a Woodcraft Pinnacle 24" straight edge that's supposed to be accurate within +/- 0.005" so that and some feeler gauges are what I used to check the fence.

It's cupped 0.01" at the infeed end and the middle and 0.008" at the outfeed end. It's bowed 0.076" at the bottom and 0.066" at the top.

Is it worth my while to contact Jet and talk about a replacement or am I obsessing over tiny amounts that won't matter as the wood moves anyway? The problem is that I'm a computer guy and in my world zero is zero no matter how many decimal places you have. Part of me worries that if I get sloppy about setup my results will suffer. Part of me says I shouldn't complain about a three hundred dollar combo machine that lots of woodworkers like. I'm clueless here. :help:

 

[Travis Porter]

Personally, I wouldn't worry too much about it. The bigger thing is if it is twisted and if you can get it perpendicular to the table. Before I would buy a new fence, I would attach a sub fence made out of say melamine or some other slick stuff and shim it out to be straight.

 

[Mike Davis]

10 minutes on a sheet of sandpaper and it would be flat.

I had a machinist friend who worked for NASA and was asked to machine a one foot thick by four feet diameter plate of aluminum for a satellite mirror. The engineer asked him if he could make it within two millionths of an inch flat. He said he could but wanted to know how they would check it. You see flatness at that level is measured by light waves that are ten millionths of an inch and when two waves are parallel the surface is flat to within twenty millionths, a factor of ten times the accuracy they wanted. When the engineer realized his mistake he agreed to twenty millionths.

So even if in your mind zero is zero in real world practicality zero can be a lot more than zero and still be acceptable.

The cup has no effect on the boards you will be jointing unless they are half the height of the fence, then they may be out of square 0.004 inch. A measure that is perfectly acceptable in wood work. The bow has absolutely no effect since the cut is on the bottom and not parallel to the fence.

So, you could spend ten minutes with a sheet of sandpaper and get it a lot closer, but it would be a waste of time as far as the accuracy of the finished wood.

 

[striker]

I'd make the phone call. I think you'll be cursing that fence for a long time to come. How are you to square up material with a fence that looks like golf green? If you're talking about 1/16 or so in bow and a serious cup, there is a good chance the fence will also have a twist to it. (maybe lay it on the in/outfeed bed & go at it with feeler gage).

Why is it like this? Did the machine take a spill or just poor machining? I'd check the bed parallel-ness also. Its important to have them co-planer as well.

You can add a sacrificial fence and remove the effects of the bow as Travis mentioned but a new machine I would see about a replacement first.

Stephen

 

[cpowell]

The basic question is how much cupping and bowing in a jointer fence is an acceptable amount?:icon_scra

Being basically a newbie I'm collecting what tools I can afford (and will fit in my one-car garage). Jet's 8" jointer/planer was too good to pass up. The price ($299.99) was right and it got almost uniformly good reviews from Amazon. I'm not planning on using it for anything large (small things like jewelry or music boxes mostly) so I don't care that the infeed table is too short to joint an 8' board. However, during setup I discovered the fence is cupped and bowed. I have a Woodcraft Pinnacle 24" straight edge that's supposed to be accurate within +/- 0.005" so that and some feeler gauges are what I used to check the fence.

It's cupped 0.01" at the infeed end and the middle and 0.008" at the outfeed end. It's bowed 0.076" at the bottom and 0.066" at the top.

Is it worth my while to contact Jet and talk about a replacement or am I obsessing over tiny amounts that won't matter as the wood moves anyway? The problem is that I'm a computer guy and in my world zero is zero no matter how many decimal places you have. Part of me worries that if I get sloppy about setup my results will suffer. Part of me says I shouldn't complain about a three hundred dollar combo machine that lots of woodworkers like. I'm clueless here. :help:

A bow of .076" or .066" would probably bother me but I don't know that it would make much difference in use. I always alternate face side in to the fence when edge jointing a panel glue up so the edge doesn't need to be exactly 90 degrees. When face jointing you are using the fence as a running surface and don't care if it is 90 degrees to the jointed bed. So face jointing wouldn't really matter a lot so long as you leave a little excess width when dimensioning. And starting with slightly oversized stock is good practice.

The fence on my jointer is off a smidge and I have jointed 6 foot length stock many times for wide panels and get seamless glue joints and very flat panels.

Edge joint some stock and see what you think. I would be much more concerned with bed flatness than fence flatness. If the joints are not seamless then call CS.

Or, if it is really bugging you, call them and see what they say.


Chuck

 

[DaveD]

I don't see how bowing or cupping is going to bother the jointing process. Now I could understand it it was twisted but then even a few thou isn't going to make a difference.

I'd worry more about the infeed and outfeed tables being in the same plane. Then again for really small pieces even that is probably a moot point unless you are trying to use it as a poor mans thickness planer.

 

[scsmith42]

I don't think that I'd be concerned over a thousandth of an inch, but I would sure be concerned over sixty-six thousands of an inch! That is the equivalent to twenty or thirty pieces of paper - a noticable amount.

If it were me, I'd have it replaced or more likely re-machined flat. But then again, I like precision tools.

Mike, isn't .066 is a lot to sand off of a metal object?

 

[Gotcha6]

1/16" = 0.625". That's a lotta sanding. That's a lotta FILING too!
Could ya hit it with a hammer? Bend it in a vise? If it's cast the answers to those questions is "No."

 

[scsmith42]

1/16" = 0.625". That's a lotta sanding. That's a lotta FILING too!
Could ya hit it with a hammer? Bend it in a vise? If it's cast the answers to those questions is "No."

Dennis, I think that you meant to type ".0625.

.625 is 5/8", and yes that would be a lott sanding!:rotflm:

 

[Mike Davis]

I don't think that would take long on a belt sander, besides I wouldn't bother with all of it - only the ends. Take a 32nd off and you'd never notice any bow. All i would bother with is the .008 warp from top to bottom if anything at all.

As I said before the bow will have ABSOLUTELY NO EFFECT on the wood in any way. As long at the fence is perpendicular to the table it does not matter if the wood wiggles 1/16 of an inch as it passes over the blades.

If you had a molding head in there then you would need to keep the wood moving in a perfectly straight line.