Thread: Jointer tables - How flat do they need to be?

I have not run wood through mine yet either.
I spoke to the supplier tech I got the 310HH from (after 3 days of hassling them) and its a common problem apparently, but he did say to run wood across the whole table and record my findings. If if does not come off flat / straight then they would replace the beds / machine for me and are "backing me 100%" on it.

Originally Posted by Blazk

I have not run wood through mine yet either.
I spoke to the supplier tech I got the 310HH from (after 3 days of hassling them) and its a common problem apparently, but he did say to run wood across the whole table and record my findings. If if does not come off flat / straight then they would replace the beds / machine for me and are "backing me 100%" on it.

Nice to see there are still places focused on customer satisfaction. I'm sure there are some out there who would give you the not our fault/it's within tolerance/other polite way of saying "we've got your money and don't care"

If it me I would run some test pieces over the jointer before I go and machine the tables flat. As you said the dish is not at the edge of the table but back some 250mm. Might be ok when you run longer pieces as to shorter ones, as the shorter ones might be lifted when you press down on the out feed.

If you see the arguments (and effort) that the hand tool guys go to to get their hand planes flat down to a fraction of a gnat's ball hair, my gut feeling is that it will be noticeable. Either that or there is a lot of wasted effort going in to flattening hand planes.

In the olden days the better cast iron machine components were allowed to age after casting by just leaving them out in the weather, the longer the better, I guess it might be comparable to air dried versus kiln dried wood, the reason for the aging was to reduce the movement of the component after machining, some of my chiwanese machines with machined/ground CI tables had/have flatness issues. Modern manufacturing where the motto is Quantity not Quality.

For starters I wouldn't do anything until I machined some wood, if there is sufficient flat area across the width of the tables after/before the cutter and these areas are coplanar you should be ok, just don't press the wood down into the low areas, let the wood ride over the low spots. If there is no joy then machining is a possible solution and surface grinding has to be an option, I would expect to be paying a bit more than $200 tho, seems to be very cheap, there'd be 2 hrs just getting your table onto and setup on the surface grinder table, I am assuming you are thinking taking your tables off the machine.

Let us know how you go.


Pete.

Doesn't really matter how flat the tables are on a JET JPT310 to start with, as after a few years use they certainly won't be flat anyway.

JET use the ribbed finish on the cast top, supposedly to reduce friction (which it does). However, this means the timber effectively rides on very narrow points/ridges of metal rather than a large flat surface. My JPT-310 is several years old, and there is noticeable wear on the outfeed table nearest the cutterhead (where most pressure is applied if you're using it properly). Doesn't affect the operation of the machine to any great extent, and these days I run stock through a drum sander as a finishing operation anyway which gets it flatter than a jointer could.

This is the reason I have resisted the temptation to upgrade my machine to a helical head - the quality of the rest of the machine doesn't justify the spend. Don't get me wrong; the HH version is a fantastic buy new for a reasonable premium over the standard cutterhead, but it would cost ~$1000 to retrofit a helical head to my machine ! I spent the money on a drum sander instead, which handles ANY grain (even burl....). Helical heads are great, but can still cause tearout on some crazy-grained timbers.

Spend a bit of time running some timber through your machine, tweak the outfeed table height for best results, and I think the results will be flat enough for all practical purposes. Where you need flatter, reach for the jointer plane.

Decided while it was cooler I would run some material through the 310HH. Only had time to test it out on one piece so I opted to run it straight down the middle across the 2 dishes and see what my results would be.
I ran a straight edge down the face and edge I saw about 8" of snipe at one end. Think this was caused by it dipping down in the dish? Would make sense sine the dish is around 8"...?

Sounds more like the outfeed table height needs adjusting to me.

To check this set the machine to take a moderate cut, then run a piece of scrap wood across the blades only taking a cut for the first 50mm or so. Switch the machine off, then run the timber along the same path you originally followed when cutting. If the outfeed table is set correctly, there should be no clearance at all as the front cut edge of the timber crosses over the edge of the outfeed table. A small error here can have a large effect on the performance of the jointer.

It can be easier to deliberately set the outfeed table slightly high at first so that your timber catches slightly on the edge of the table after the cutterhead, then wind it back tiny amounts at a time until you JUST get a smooth transition as the front edge of the timber hits the edge of the outfeed table.

Technique can also make a big difference with a jointer - as soon as enough board has passed across the blades, you should be applying more pressure to the timber on the outfeed table just past the cutterhead than to the timber remaining on the infeed table. The trick is keeping the pressure at this point as the timber moves along.

My JPT-310 can produce dead flat boards, but I can easily introduce a slight curve just by applying poor technique (pressure in the wrong place at the wrong time).

Originally Posted by Mr Brush

Sounds more like the outfeed table height needs adjusting to me.

To check this set the machine to take a moderate cut, then run a piece of scrap wood across the blades only taking a cut for the first 50mm or so. Switch the machine off, then run the timber along the same path you originally followed when cutting. If the outfeed table is set correctly, there should be no clearance at all as the front cut edge of the timber crosses over the edge of the outfeed table. A small error here can have a large effect on the performance of the jointer.

It can be easier to deliberately set the outfeed table slightly high at first so that your timber catches slightly on the edge of the table after the cutterhead, then wind it back tiny amounts at a time until you JUST get a smooth transition as the front edge of the timber hits the edge of the outfeed table.

Technique can also make a big difference with a jointer - as soon as enough board has passed across the blades, you should be applying more pressure to the timber on the outfeed table just past the cutterhead than to the timber remaining on the infeed table. The trick is keeping the pressure at this point as the timber moves along.

My JPT-310 can produce dead flat boards, but I can easily introduce a slight curve just by applying poor technique (pressure in the wrong place at the wrong time).

In regards to adjusting the out feed table, when i loosen the black star knob and try and move the leaver nothing happens. Is this becuase you have to release the lock nut on the other side as well? The manual wasnt very clear on this ?

Originally Posted by Colin62

If you see the arguments (and effort) that the hand tool guys go to to get their hand planes flat down to a fraction of a gnat's ball hair, my gut feeling is that it will be noticeable. Either that or there is a lot of wasted effort going in to flattening hand planes.

A) There IS a lot of wasted effort going into flattening hand planes if it's being done to try and get a flatter result on the timber. If they were good enough from the factory for a man to make a living with them, they're good enough for the hobbyist of today.
B) Deviations from flatness on the smaller surface of a hand plane taking shavings of fractions of a mm will potentially have a much larger effect than a large machine table taking passes of several mm

If people want to lap their hand planes to a mirror finish and to thousandth of a mm precision that's fine, but don't tell me it's for any reason other than wanting a flat, shiny plane.

Originally Posted by Mr Brush

Doesn't really matter how flat the tables are on a JET JPT310 to start with, as after a few years use they certainly won't be flat anyway.

Hope it takes more than a few years for table wear to be noticeable. It's taken 60 years and countless kilometres of timber to wear a 0.5-ish mm dip in the thicknesser table at work. And that's with spring loaded pressure rollers, not just hand pressure of jointing.

Blazk - you are doing it right, and the outfeed table should move relative to the cutterhead. There should be no need to loosen anything else. In case you don't have it, download the infinitely more useful USA manual for the machine here:

http://content.jettools.com/manuals/708475_m.pdf

elanjacobs - for a machine with solid table, I agree with you. I've used ancient Wadkin jointers that have minimal wear in the top after 40 years industrial use. The point I was making is that the ribbed cast tops wear much faster, as there is only a tiny amount of metal in contact with the timber. If I had my time again, I'd avoid this type of surface like the plague. It may offer lower friction due to less surface contact, but I'd rather have a flat solid surface and apply wax from time to time.

The table surface on my JPT-310 is also a very porous casting (good for soaking up a bit of wax....), but I'd think twice about machining it flat.

Ah, missed that bit. Yes the ribbed surface is a problem, especially if the casting itself isn't top notch, but I'd guess it's cheaper to manufacture. A planed/scraped finish has the same low friction effect with minimal wear (the 'ribs' are fractions of a mm in height) but you don't find many companies doing it any more as it's prohibitively expensive.

They don't say that in the brochure , but I'm sure you're right about the cost of manufacture. Several other cheaper combo machines also feature ribbed tops as well.

To get conventional flat tables in this class of machine, it looks like you've got to step up to a Hammer A3-31......

Sometimes the old machines are actually the best value for money, as long as you check the start of the outfeed table for excessive wear. Something that has spent a long and hard life at a timber yard is probably best avoided though !

Cheers