Flattening TS top

[Scottdimelow]

As I've just mentioned in another post, I've just bought and old table saw. Checking the top with a straight edge and it's more of an upturned bowl!!

Using a square against the blade there is quite a difference on either side.

Has anyone had a top flattened?

TIA

 

[Water-Mark]

I have an old 6" planer that had non adjustable tables out of alignment and after playing around with shims and spacers i managed to stick a piece of ply on the outfeed table to level them.

It'll never be a permanent solution but it has made it a useable machine.

 

[DennisCA]

Sounds like a job for a machinist to me.

 

[marcros]

how far out is it? A machinist could probably correct it, assuming that there is sufficient meat in the top. But at what cost is the question. From the other thread, you also need to make or have made a guard and riving knife, so if cost is a factor, I would be tempted to do as water-mark suggests and make a sub table to fit on top. That may give you fence problems, however. It looks quite a nice saw, but could be a money pit if you are not careful. That is money that you wont get back if you come to sell it, because it is only bring it up to a standard level of completeness/spec.

 

[n0legs]

Blanchard grinding is what you need to flatten the top.
Findng someone to do it and cost will be the big problem though.
How far out is it ?

 

[Scottdimelow]

Yeah, I imagine it would cost a fair bit. I found an article online that mentions shimming the trunnions to correct warpage. I'll give that a try first.

It's this one
http://home.comcast.net/~jaswensen/mach ... /flat.html

 

[dickm]

What's the top made from, how big and how bad is the bowing? If it's not a huge cast iron table, then filing plus hand scraping with an engineering scraper is not out of the question. Certainly getting it to "woodworking tolerance" shouldn't be impossible. Even easier if it's alloy.

 

[Scottdimelow]

Thanks guys, sorry I've yet to get any pics. From front to back it's about 1mm out, the the high point in the middle. Left to right, just on the centre section it must be 2mm again the sides drop away.

Could it be the extensions? After being bolted on for years could they cause the middle section to bow?

I like the idea of scraping it, maybe use a flap disc in the grinder too. It has a lovely machined texture to it though, I wouldn't want to loose it lol.

It's cast iron, couldn't tell you more than that to be honest.

 

[n0legs]

Given it's the centre "up" maybe unbolting it from the support frame and shimming it up past the height the where the mechanism is mounted to the top.
The weight of the extensions would be a fair guess to the cause of the sagging I'd say.
Any idea how it's all held together?
Flap discs can be a bit aggressive and could quite quickly create hollows.
Like Dickm said earlier a file and a scraper could be the way to go, time consuming but effective, but also very controllable.
How big is the top on it's own? I'm wondering could a motor engineering works do it on their cylinder head machine.

 

[bugbear]

It all begs the question of "what can you trust. Some processed involve using a power tool table as a reference or tool to flatten a hand plane, because of its "obvious" accuracy...

BugBear

 

[Scottdimelow]

Well, I couldn't resist going out to the workshop in my dressing gown and taking some pics.

The main top is 590mm wide and 680mm deep. The extensions add a further 200mm either side making it about a metre total.

In the first pic with the light behind the straight edge, it's showing the worst part. I've drawn red marks on the the straight edge, between those marks there is a gap of 1.3mm.

In the last pic you can see a red outline, that's where the high point is. I did a test cut yesterday and on a piece about 500mm long, the first 100mm was out of square then it corrects itself. Obviously this is an issue.

 

[n0legs]

Personally I would look at getting it machined if possible. From the pics it seems quite a way from flat.
I see what you mean about the machined pattern, very nice.

 

[heimlaga]

I am known for filing and scraping stuff others wouldn't but in that case even I would bring the table to a machine shop to have it flattened. Just like I did with my worn thicknesser table. It had planed such amounts of wood in it's life that the wood had worn down the cast iron about 0.5 millimetres at worst. You will loose the planer marks but they serve no practical purpose. They just came from the machining process. Metal planers of the type that were used to machine theese tables are very rare nowadays. They have mostly been replaced by blanchard grinders in industry.

 

[Scottdimelow]

Well I emailed 5 local engineering firms, not one reply. I am tempted to grind some of that hump out though, what's the worst that could happen

If it goes horribly wrong I can always add a piece of mf-ply, it would be quite easy to get that level I think.

 

[RobinBHM]

I once flattened a surface planer outfeed bed that wasnt flat. I used a 4" belt sander. The belts dont last long, I bought a load of 40 grit belt. Then worked through the grits to get the shine back. It takes a loooooonnnng time!

To achieve the flattness I just used a straight edge and a light, similar to your images.

 

[dickm]

Well I emailed 5 local engineering firms, not one reply. I am tempted to grind some of that hump out though, what's the worst that could happen

If it goes horribly wrong I can always add a piece of mf-ply, it would be quite easy to get that level I think.

A lot of the smaller engineering companies, the sort that might be interested in the job, aren't very good on email! Better to ring them, or even better, drop in to see them.
We are a bit spoilt up here, as there are lots of small jobbing shops who do sub-sub-contracts for the oil industry, and will turn their hand (or machine) to most things. A guy just down the road milled out a recess in the top of my CI router table to take the Elu 177 and charged the princely sum of £20 for it. That doesn't really help in Rossendale, but you should find that the personal touch helps.

 

[Scottdimelow]

Cheers Dick, I know what you mean. I have used a local company for a bit of pipe threading, don't think they'd be able to do this but I'll check.

There are quite a lot of companies but as you say, websites and email doesn't seem to be there strong suit.

 

[Scottdimelow]

Well, here is my solution to my anything but flat cast iron top. Make a new one out of concrete!

I have a mild obsession with concrete, it's awesome!

It turned out very well, I checked the mould for flatness before pouring, and I could only get a .1 gauge under a couple of spots.

I've not had to grind or polish, just gave it a coat of wax.

 

[deema]

I wouldn't have thought about casting a concrete top, looks brilliant and I can't think of a single reason why it shouldn't be brilliant.

 

[Scottdimelow]

Cheers Deema, that was my thinking entirely. This is high performance concrete, glass fibre re-enforced and probably about 13-15000 psi.

It's actually lighter that the cast one!!