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billr
10-17-2003, 07:18 AM
good morning.

a while back i bought a different mill. the table has some dings in it. lots of dings.

i have stoned the high places down, but that will not take the dings out. i would like to be able to have more of a flat surface to work on.

so, does anyone have any suggestions as to how to go about this?

cheap and easy would be better than expensive and difficult. i have thought of buying a big face mill and doing it myself but am led to understand that i cannot do that. it seems to me that the surface would be as accurate as the machine is, but i would rather do it 'right' and be done with it.

i would be grateful for suggestions, advice, etc. thanks in advance.

peace.
bill

Dr. Rob
10-17-2003, 08:58 AM
Same problem here. Well, no problem since I generally use the vise anyway, but I wouldn't mind a remedy.

A while back, someone said they'd used epoxy filled with steel filings, and it had held up for twenty years.

Why wouldn't face milling work? (does the spindle reach the entire table? Don't think mine does.)

jr45acp
10-17-2003, 09:03 AM
I haven't tried this myself, but am considering it. I remember a suggestion where the dings were filled with JB Weld or Marine Tex or a similar product. Then, a very light draw filing was done to match the repair to the mill table surface.

Seems logical.

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John B

billr
10-17-2003, 09:13 AM
Doc Rob,

i don't know why it wouldn't work. i could reach all the table with one move of the ram and one of the rotation. the proper term eludes me. this is a cincinnati mill and has a thick table. it looks to me like i would have to maybe take 0.050 off of it. maybe a little less. it has been a while isnce i measured.

i am sure that it would be better to have it surface ground, but alas, i am poor and that sucker is heavy. also probably not anywhere very near that can do that.

i have read about the guy with the j-b weld, but i don't think i want to do that to my mill. i would much rather have a nice flat [reasonably smooth] table that was all iron. i suppose i am eccentric.

so. does anybody know why this won't work?

would you please tell us? thirsty and inquiring minds want to know.

thanks. happy weekend.
bill

John Stevenson
10-17-2003, 09:33 AM
I bought a Bridgeport a while ago with a few nasty grooves in where some twonk had been milling with a 3/8" end mill and no packing and had marked the bed in about 4 places.
I contacted Bridgeport in the UK who said you can take 150 thou off max and I sent this table in to be ground.
The company I used have a Lumsden grinder what I belive you call a Blanchard grinder in US speak.
I told them to pack up off the vee ways and minimum off to clean - stop at 0.150" if not.

Upside of this process is it's quick and cheap. Down side is it leaves the characteristic circular grinding marks of a Lumsden / Blanchard but if you ask them to leave it on until it sparks out they aren't as bad. In fact after a while when it gets a used patina on it they fade in a lot.
My Bridgeport table cost me about $25 in US money it's not an expensive operation and they had to take about 80 thou off although it looked a lot worse.

I often pick surface plates up from the scrap yard for a few pounds that are either well dinged or rusty and have these done for about $10 each. OK so they are not hand scrapped grade 1 but they are flat and clean, plenty good enough for anything other than scraping.

Who's to say that that old surface plate with all the pristine scrape marks on it is still flat after all these years ? I know mine is.

John S.

Rustybolt
10-17-2003, 10:50 AM
I wouldn't recomend doing it on the machine. Unless your machine is exceptionally tight you run a good risk of milling a crown in the middle of the table.With that much weight hanging off one end.

Paul Alciatore
10-17-2003, 02:04 PM
<font face="Verdana, Arial" size="2">Originally posted by Rustybolt:
I wouldn't recomend doing it on the machine. Unless your machine is exceptionally tight you run a good risk of milling a crown in the middle of the table.With that much weight hanging off one end.</font>

This brings some thoughts and questions to mind.

So the table will bend when moved to it's limits. Anyone know how much? Doesn't it do this anyway whenever we work with it?

I know the gibs would have to be extra tight for any such operation to prevent any rotation due to any play in the dovetail. As tight as possible while still allowing the table to move would be best.

Question 1: Assuming a perfectly flat table could be made, persumably on a much larger machine, would not that table also bend when traversed off center? Would that bend not be exactly the same as a table milled flat on it's own machine?

Question 2: Since while milling the table, all cutting would be done diredtly above the intersection of the two slides, wouldn't the distance from the spindle to the table remain the same while milling all points of the table. It seems that this is a basic advantage of the standard arangement of a vertical or horizantal mill. Again, this assumes very tight gibs to prevent anyh rotation due to play in the dovetail.

Question 3: After milling it most of the way, couldn't you mount an abrasive wheel on the spindle to provide a better surface finish? Most mills have slower speeds than a grinder and it will take longer but wouldn't it work?

Of coursd, my first choice would be to ignore the dings unless they do interfere with work on the machine. After all, we mount every workpiece over slots that are 3/4" to 1" wide every day and they pose no problems. I have two chucks that are full of dings and accidental cuts on their faces - not my doing, I assure you. They are old and not the most accutare, but they work. So I use them. I also have a new, unscratched, undinged, uncut chuck. It also works. I myself also have a few dings, scratches, etc. I still work - most of the time. Perhaps that's why I don't worry about tools that ate less than perfect in a cosmetic sense. Seems like they also have a place in my world.

Paul A.

bikenut
10-17-2003, 03:00 PM
Don't ruin your mill by taking a cut on the table. Stone the high spots, and don't worry about the dings. They will never come into play, unless you are pulling a part down into them (wrong). Use parallels if you are clamping a part to the table. The dings look ugly, but they won't hurt you if you pay attention to where you clamp and what you are doing.

darryl
10-17-2003, 03:33 PM
I agree that the dings don't generally interfere with the accuracy, as the workpiece will generally cover the dings, and sit flush with the remaining flat, factory surface. It's the high spots that will get in the way. Sound like a good idea to use parallels anyway, whatever works to ensure that the cutter doean't cut into the table. If resurfacing will give you peace of mind, or an actual increase in the accuracy of the table surface, go for it. If you do it yourself, it would seem at first thought that the final surface would be 'matched' to your machine, with no deviation in spindle to table distance at any point on the table, and any work you do on it should be as accurate. I don't know about the better machines, bridgport, whatever, but my cheap mill will change that distance by about 3 thou as the spindle heats up. I would like to think that I could run it to equilibrium temp, then with all gibs snug, and a fresh clean and relube on the ways, etc., resurface grind the entire table, and end up with a more accurate surface, even if it's not as pretty as a pro regrind. I would like to hear more about the hazards of doing this at home, vs taking the table out for refinishing. Would a separate grinding motor and wheel, clamped in the non-rotating spindle be a better way?

Evan
10-17-2003, 03:40 PM
I'm thinking that although the spindle to table distance won't change the angle of the table relative to the spindle might, a bit, when it is at one end of travel and overhanging. One could always machine a flat on the top of a stick of aluminum and see how flat it is. That should give a good idea.

Paul Gauthier
10-17-2003, 04:02 PM
I gotta go with John, take it off and have it ground. Make sure the poeple who do the grinding know how to grind a B/P table. It must be properly supported. Blanchard or surface grind doesn't really matter they just look different.

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Paul G.