Making a new worktable.

MrCrankyface

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A bit of a sidetrack from my workshop thread (Workshop).
Work surfaces has been an ongoing struggle in my garage, the first table was too weak, the second too large and space inefficient.
So this is my third try...

I found these two cast iron plates on the Swedish equivalent of craigslist and decided they'd be a good start for it.
They're both 400x800 millimeter in width and length but one is 140mm thick and the other is closer to 105.
Neither is completely solid, underneath they have a hollow part, the thicker with some webbing like most cast iron surface plates have.
I calculated that the thick one weighs in at around 222kg so it's a difficult piece work with. :grin:
IMG_0920.jpg

Since both plates have been beaten up quite severely I wanted to try and deck them in my mill.
My mill has a movement of around 230Y and 630X on a good day so I'm going to need do this in several setups.
But first to even get it up on the mill I had to experiment with the engine hoist.. The thicker one already had some bolt holes in the side I could wrap the sling around.
IMG_0922.jpg

The sheet itself is bigger than the saddle casting.. :grin:
Just the weight is causing quite a lot of issues for my non-perfect CNC conversion.
The Z motor keeps stalling from the combination of a sticky Z axis and the added weight and the Y axis gets serious problems moving when all the weight is cantilevered out to the left.
This makes it difficult to do fine adjustments or efficient movement patterns since I have to manually(with a plier) help the Z stepper motor to set my depth and can only (reliably) move Y when the weight is somewhat centered on the saddle.
At least it's giving me a lot of notes on what to improve upon.
IMG_0923.jpg

The milled surface is pretty much the full movement of the previous setup, I've now moved it as far left as possible so I can reach the other side of the plate.
It's so far to the side that I can't use any T-slots and have to resort to carefully clamping around the entire table, with a wooden piece inbetween to not damage the ways.
So far I've only been using a 40mm corncob style endmill.
IMG_0936.jpg

This is what the surface finish is like with the endmill.
Tramming was a tiny bit out in the X rotation axis whilst side to side tram was great.
You could just about feel an edge between the old and new cut, it's probably slightly below 0.1mm.
Cutting it this way took a lot of time since I didn't have the guts to speed up the mill very fast from fear of unneccessarily dulling it.
IMG_0928.jpg

For those of you that are into 'memes', this really made me think of "you versus the guy she told you not to worry about". :grin:
Kinda hidden in the background, I've drilled and tapped 5 holes in the center pocket, this will aid both lifting the plate and fixturing parts on it later.
IMG_0943.jpg

Many hours later, thick plate has been decked. I did a couple of mistakes and I think the entire plate is probably only within 0.2-0.3mm but was so tired of it that I decided it was good enough for now.
I still need to remove a bunch from the bottom to make it equal thickness to the other one, which might cause the plate to shift a bit so will most likely redeck it again.
IMG_0949.jpg

Had I been smart I would've started with the small plate but I learnt a ton on the big one so maybe it was good after all.
Swapping out the large plate to the small plate, I first flattened the bottom and then started flycutting top.
I was super picky here and removed maybe 0.2mm at a time, each time adjusting my tramming a miniscule amount until I got the cuts to blend perfectly into eachother, EXTREMELY time consuming.:rolleyes:
Of course I crashed the mill, ruining my tramming, maybe an hour after it was perfect.
At least the flycutter is giving a better finish, takes around the same time as the endmill since my feed is much slower but the width is much larger.
You can see the head and tool in the reflection of the plate, something that definitely wasn't possible on the other plate.
I found that I have to go up quite a bit in surface speed, above 120m/min to get a good surface, but this is also very close to making sparks so I save it for the fininshing cut and spin slower for roughing to not dull the tool.
IMG_0957.jpg

It's interesting with heavy things like this because even just flipping them over is a difficult task.
I drilled and tapped for M12 bolts in the sides of both plates and made an improv lift bar.
It's too short for turning it midair(chains get caught) but at least it made it a ton easier to lift it slightly from the floor and carefully start leaning it over.
This is definitely one of those jobs where "slow and steady wins the race".
Rather make a tool that makes the job easier, than try to do it fast and dangeorus(ie manhandling it over which I tried on the smaller one).
IMG_0960.jpg

Finally on the mill with the bottom up, I gave my 25mm insert endmill a try for roughing.
I need to remove nearly 4cm of cast iron, each edge being 5cm wide and I definitely didn't feel like wearing down my regular endmills for this when inserts for this insert endmill are dirt cheap on ebay.
To my suprise it also loves high feeds and speeds.
From ~200rpm and 150mm/min with the 40mm endmill @1mm doc I could go up to 1088rpm and 500mm/min @ 2mm doc, just seeing the spray of cast iron chips was pretty fun and it left a superior surface as well. :grin:
Even at these speeds it takes quite a while and the stepper motors still stall out from time to time, leading me to have to reset the control software etc.
I'm going to scrape the machine in, change to ballscrews, gear the steppers even stronger and build in a better oiling system in the future so hopefully this won't be a problem after that.
But for now it's a half-manual process where I set the Z by hand and then let it run a short program that mills the shown surface before I move the plate on the table.
Hopefully I can finish these plates up soon and move on to the actual table build!
IMG_0962.jpg
 

MrCrankyface

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Thanks!

Spent nearly 4 hours yesterday finishing that cut and a second setup.
I decided to calculate how much material I was removing, since it felt like it was taking forever.
Apparently I've converted around 13kg of material into chips .... :grin:
13 more to go.
image0.jpeg

On this setup I can fixture it better and it's more centered on the knee so no more stalling issues.
I've really tried to optimize my speed and feeds but I think I'm very close to my fastet reliable settings.
Around 1088rpm, 500mm/min, 2mm doc and a 96% stepover.
I have enough horsepower for 3mm(I tried) but the cutting pressure becomes so high that it starts pulling the sheet out of the clamps no matter how tight they are so 2mm felt like a safer bet.
Here's a short clip of a run, at the end of the program it first lowers the piece a bit to get the sticky Z moving, then raises it back up to -2mm Z for the next cut.
For jobs like this I really love having the CNC features, despite the large backlash in old worn screws, especially since I have to run this same program around 16 times to get down to depth.
 

vtcnc

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Serious endeavor! Craigslist finds will push us out of our comfort zone into a creative world! Well done. Looking forward to seeing the final table!


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MrCrankyface

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Thanks! And yes, sites like that has gotten me into most of my adventures... :grin:

Been too tired to do milling today so instead I've been drawing up a frame design.
My initial idea was going with an all steel frame but my budget just won't allow it and I don't have that kind of amount of scrap laying around.
Instead I designed a frame that should be quite beefy around C24 timber.
Buying all these studs and a sheet of plywood is going to be around 20% of the cost of the steel version, biggest drawback is it's bulkier so less storage in it and probably takes longer to make.
Kj1WtPw.png

With all the plywood pieces removed, it's a bit easier to see the actual frame.
The left open area will have full extension drawers at around 70cm wide and the right side will most likely just have a door for storing tall items(dial test indicator stand etc).
nI2o9Dy.png
 

vtcnc

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Thanks! And yes, sites like that has gotten me into most of my adventures... :grin:

Been too tired to do milling today so instead I've been drawing up a frame design.
My initial idea was going with an all steel frame but my budget just won't allow it and I don't have that kind of amount of scrap laying around.
Instead I designed a frame that should be quite beefy around C24 timber.
Buying all these studs and a sheet of plywood is going to be around 20% of the cost of the steel version, biggest drawback is it's bulkier so less storage in it and probably takes longer to make.
View attachment 367805

With all the plywood pieces removed, it's a bit easier to see the actual frame.
The left open area will have full extension drawers at around 70cm wide and the right side will most likely just have a door for storing tall items(dial test indicator stand etc).
View attachment 367806
The word "stout" comes to mind when reviewing your sketches. I like it. Have you considered making this mobile?
 

MrCrankyface

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The original idea for this worktable was to have it on wheels, then I moved to the idea of having it on legs but lowerable wheels if I wanted to move it.
Having it always on wheels doesn't give me the rigidity I want and having lowerable wheels for such a heavy table adds a bit more complexity than I want.
I'm currently considering having it "as is" on maybe 4-6 hockeypuck feet and then using my engine hoist(lifts up to 2t) to move the table around if there's a need.
Most likely the workbench will just sit in one position 98% of the time, but for those weird jobs I might need the space where it sits or need the bench elsewhere.
 

MrCrankyface

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I hope so! :grin:

I had this brilliant idea last night to not mill the cast iron down but rather part it.
So on I went with a saw once I got home from work today.
It would've been a pretty quick process if it wasn't because the mill kept stalling out(the stepper motors losing position, requiring a reset).
I really hope this will be solved with scraped ways, ballscrews and 3:1 gearing instead of 2:1.

And now I have 2 chunks of cast iron!
My only regret is not doing this to the entire thing, the smaller chunk could be real handy for future projects.
Now I just need to take a tiny cut on the large sheet to make sure it's perfectly flat.
IMG_1076.jpeg
 

mattthemuppet2

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nice! That's a very useable chunk of CI.

For the bench, looks plenty stout enough. Only suggestions I would make is to have the 2 large'n'heavy plates over the center support instead of over the unsupported span and to put some diagonal braces between the back uprights. You have a relatively tall and heavy top sitting on 6 relatively narrow (with regards to left/ right looking at the front) pads, so other than a plywood back you don't have much resisting side to side loads.
 
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