Flattening machine tables

[marcus]

Just noticed this new forum — brilliant!

Just wondering if there is an economic way to flatten cast iron machine tables that are warped? My bandsaw was ex-demo and the table has never been flat. I've been quoted a silly price for a new one. Would be great it was possible to fix the one I have. I don't mean doing it myself, but is there someone I could send it to?

 

[marcros]

how out of flat is it? I wouldnt have thought that setting it up and running it on a surface grinder would be too long a task for a machine shop.

 

[Keith 66]

Slideway services have a big surface grinder capable of doing lathe beds, it depends how badly its warped.
Other way would be leave it as it is & bond a sheet of plastic to the top. Im thinking tufnol. acrylic or nylon whaever you can find cheap if its say 8mm thick put it face down on a known flat surface & bond the warped table to it with polyurethane sealant such as PU40 or Sikaflex or equivalent, dont clamp it so as to pull the table out of shape. Proper bodge but might be worth a try!

 

[marcus]

Thanks, it's just over .5mm out of flat across the width (see pic):

 

[marcros]

where are you in the country/world marcus, might help with suggestions.

if he doesnt pick up the thread, might be worth dropping wallace (mark) or jack from canada (you will find his user name on one of the restoration threads) a PM. They have both done some restorations and may well have done some flattening.

In the mean time http://wiki.vintagemachinery.org/Flatte ... faces.ashx

 

[CHJ]

Trouble with machining any cast surface is that it is just as likely to move in a different direction due to release of locked in stresses.

0.5mm? be pushed to cut any piece of wood to that level of accuracy on a bandsaw and I personally would not be trying to achieve it on a metal cutting saw either.

 

[Jacob]

My Startrite 352 was never flat. Nor was the replacement table they sent. The remedy was a few carefully placed shims/washers/wedges on the underside fixings.

 

[ColeyS1]

Axminster seem to get over the problem by having a tapered metal dowel that pushs into hole that drilled on the joint- clamp em level first before you drill it though :lol:

 

[marcros]

i wondered what that hole and handle was for that i seen on some pictures.

 

[CHJ]

Trouble is that type of alignment only pulls the surfaces back into the same plane as when it was machined, it does not stop a dip or rise across the slotted area if it subsequently forms.

What type of fence track do you have along the front edge, can you incorporate a stiff steel angle along the bottom front edge to force the slot area up.

My Sip machine relies on an alloy extrusion fence track bolted from underneath to maintain the alignment, but the table is naturally flat in the first place so no loads involved.

 

[marcus]

Thanks for the link Macros, very interesting!

Jacob:

The remedy was a few carefully placed shims/washers/wedges on the underside fixings.

Sensible idea, but doesn't work in this case — I tried it but the fixings are in the wrong place....


The tapered dowel idea is potentially a good one and would help will have a think about that!


The fence is attached to a bar which has only two attachment points, so it's not much help.


I know bandsaws are usually thought of as machines for rough cutting but mines a pretty good one apart from the table (Startrite 440R); I run a wide TCT blade in it, and it can cut with great accuracy when I'm using the fence as a guide: for example doing joinery cuts or sawing wide veneers. It would be nice to have the same accuracy for ripping though, as it IS my rip saw — with the TCT blade it's almost as fast as a table saw and gives a very clean finish, but it's not as dependably square as I would like when ripping thick stock because of the table issue....

 

[CHJ]

Instead of trying to flatten the table is there any mileage in setting it up perfectly horizontal with the blade access gap plugged and floating a floor levelling epoxy over it ?

Would not render the mitre slot unusable I would have thought.

 

[jasonB]

You can buy special epoxys for building up machine ways etc which may be worth a try, rather than try and feather it out I sould coat a flat surface in teh epoxy and then stand the table face down in in with say a 1 or 2mm shim in each corner so you get a layer of teh epoxy over the whoel surface.

Moglice is one brand

 

[Dangermouse]

I think your asking too much of a bandsaw. but have you thought of tapping a threaded hole each side of the slot and bolting a pice of flat bar across, underneath. My Wadkin has this made from new. It holds the table flat across the slot. I've never measured it, but looks perfectly in line by eye.
As has been said .05 mm is pretty tiny, i'd cut to that and finish by hand plane. Dont know why you need to be perfect right off the saw, I was taught thats never the right way.

 

[marcus]

.05 mm is pretty tiny

It's not .05, it's over .5, which is quite a lot! I know a bandsaw is capable of the accuracy I need, as I've used ones that were that accurate. — a heavy bandsaw that can tension a wide TCT blade is quite a different beast to the usual light-weight ones.....

Don't know why you need to be perfect right off the saw

Time is money!

Have you thought of tapping a threaded hole each side of the slot and bolting a pice of flat bar across, underneath.

That would help a bit but I don't think it is possible on mine as the casting is too thin near the slot. Also most of the problem is not in the slot — the table itself is bowed right across the width....

 

[marcus]

I'm liking this epoxy levelling idea. Are there any obvious downsides/potential problems with doing this? Can anyone recommend any brand names?

 

[heimlaga]

When i bought my 24" combination machine the thicknesser table was worn down about 0,5 mm in the middle. Apparently it had planed a lot of wood in 50 years of service. A local machine shop surface ground it flat for me. I think they charged 60 euros or something like that.

Another more laborios way would be to find a flat surface that can be used as reference and smear it with mashinists blueing and put your table opside down on it and then hand scrape down all blue spots on the table. This would take a weekend but it can be done with good result. The scraper removes about 0,02 mm at a time. Scraping is not very difficult.

 

[dickm]

Another vote for hand scraping - it's tedious but it works

 

[marcus]

Sounds promising! What tool do I use for the scraping?

 

[heimlaga]

A maschinist's scraper. There are several types of them but for scraping flat surfaces one is enough. A scraper for flat surfaces looks like a flat file without teeth with sharpened edges around the end. The tip is usually made from carbide soldered to a steel body but older ones were made entirely from steel.
Mine has the text "Sandvik Coromant" on it and I paid 1 or 2 euros for it at a flea market but they are not too expensive as new either. They can still be bought new. Theese days scrapers are mostly used at machine shops for rebuilding worn out metal lathes.

If you are right handed you hold it at about 45 degrees to the surface with your right hand holding the handle and your left hand holding the blade near the tip. That you push it forward and downward with quite a bit of force. The corner of the tip then scrapes away roundabout 0,02 mm of the surface. As it is hard to keep the cutting depth even one should if possible scrape in a criosscross pattern so that when a surface has been scraped all over from one direction the next cut is taken at 90 degrees to the previos one. Otherwise the surface becomes wavy. Only cast iron can be scraped while aluminium and mild steel cannot.

Right now I have some rather extensive scraping going on as I rebuild an old morticer. Feel free to ask questions.