so here's a rather long post and if its too long please just skip it..
tape has thickness but if you go into packing tape , its probably only .005" or so. So you can get it really close and then just be careful once tape is not there. on wood fillers I'll often use the tape to guide a cabinet scraper. you can always just change tape if you find it wears out. often my rule of thumb is to keep any repair area as small as possible, no point expanding into areas that dont need repair.. with wood fillers the smaller the repair is the less its likely to be noticed. on slate of course the cloth covers any color etc. with wood , spreading fillers can sometimes affect the results of the color of finish, absorption of a topcoat or stain etc. lots of people like bondo or you can use glazing putty if its very thin, the glazing putty doesn;t need catalist so you aren't needing to do mixes but its not good to put it thick, might chip.. I liked the durhams hard rock putty, but use what you like best. The durhams might not be the best if you put it thick.. but its sort of watery stuff that spreads thin easily..
any greasy or glossy area might bget a better bondo if its roughened up a bit before bondo, to get a better "hook" there are different types of bondo, some sands way easier. If you need to knock off high spots in bondo you might try a sharp cabinet scraper. bit of a knack to using one right but they can often do what sandpaper can, if its a flat surface. you can buy them or if you want to make one you can use a chunk of a handsaw blade. ( cut it with a zip disk) it needs to be a metal you can file, but a bit springy. I'll just take a mill file and draw file it a bit to sharpen it square, sharp like the corners of an ice skate. If i want to take a bit more off , on wood. I'll run a screwdriver over the edge pushing down and form a hook on the edge then it will be more agressive and remove wood faster.
for finer work you cna use a thinner blade, Ill usually just hold the balde and you dont eed all the accessories but the holder helps, especially for learning or pulling itowards yourself, normally its a tool you push away from you while forming a slight a slight bend in the blade. anytime I use a hand plane Ill use a cabinet scraper and it replaces sanding in many cases. they will pull of fine shavings without digging into the grain,, a plane or a jointer or thickness palner sometimes has a tendancy to tear out the grain. especially if the grain is confusing and there there is no real direction ,, otherwise one direction ( in wiood) will often cause more tearout than another direction. Of course any filler has no grain or direction.
Sandpaper has a tendancy to pull out the softer parts of the grain, on wood, a cabinet scraper just works upon what it touches so it flattens things out very nicely. often a cabinet maker will keep one in his shirt pocket. they are very handy and simple.
with wood fillers and maybe with bondo you can have some shrinkage in the filler so sometimes I find it easier to put it on a bit thick , I put masking tape either side of a crack . kheeping the tape tight to the area,, then i can use a putty knife to press it into the crack , and over fill just the crack. that way Im not contaminating the surrounding area but can use the knife on its flat to force stuff into thin cracks.
then pull my tape, then when good and dry use a cabinet scraper to level it, that way im not going back with a second coat due to the problem of shrinkage bringing my filler below surface level.
here's a set of tools, which you dont need but if you do lots they can be handy. the file holder lets you sharpen without going to put the blade in a vice, but not really a necessary item.
Discover the Veritas Scraping Set. Buy this product now on our Lee Valley online store.
www.leevalley.com
I have a special tool that was used by saw filers ot flatten saw blades if they are warped.. its simply bacically a flat straightedge, about 1/16" or so thick with one edge ground true..
If I take that and put it near where slates meet, and turn int in a circular way, then you can feel it drag on the slate.. if it is perfeclly coplaner at the joint, then you can feel the high points easily and you can also check if it rocks at the point where slates meet.
If I lie a strong flashlight behind it and study the glint of light coming under from the other side it helps you see any difference visually..
what I found helped was to take a straightedge, I used a 6 foot level. then put a playing card under it at 4 pionts, two on each slate.. then just check if the cards are loose anywhere.. if a card is loose then you can shim the slate.
with the machinists level you can put it on top of the carpenters level to check a longer stretch, like lay it across both slates.. put it along the table and acoss as you adjust.. important that the carpenters level is true, not an old bent one. if you start flipping it end to end or flipping it over you may detect any slight bend in your level..
with he machinists level , the way you check it , just turn it around, set it in the same spot,, if the bubble finds a different spot the level is out of adjustment.. If you dont want to adjust the level itslef , just split the difference.
you should be able to get it so you see the machinists level tip from the bubble on one end to the other by placing a playing card under the longer carpenter's level on either end. once you are within that then you are starting to split hairs and geting very close. Im talking about a differnece of a playing card thickness over 6' moving thebubble.
putting a pool ball on the slate with no cloth shows a lot by the way the ball rolls when its moving slowly.
I wouldn't worry about the machinist level too much until you are at the point that the ( less sensitive) carpenters level reads true, get it close before getting overly fussy.
on mine i had some bow it the frame. I think it was made that way intentionally back in 1916 and anyway,, some warp over the 120 years or so is expected.. I levelled my center slate first, then checked that i had enough room to shim under the end slates.. if the center slate is lower, you can trap yourself because you can't get the ends any lower than the frame ( unless you plane the frame down)
so if that seems to be the case I'd set the center slate up a bit higher so you have room for adjustment shims when you get to levelelling the end slates..
in the end you can take the machinist level and mark with chalk which direction the slope is and check various points, then you are checking the slate itself and you may find some irregularities, then all you can really do is start splitting differences.
I found a slight bow in one near where they mate and filled a small area , very thinly with the hard rock putty, but that was very slight. I did not want any difference in height at the joint as that might affect the ball. so how they mate up is as important as overall being perfectly level.
I'm not a pool table mechanic by trade, but have some experience doing precision levelling.. A guy that does this for a living may use some different techniques, or have different advice but thats what I did and felt happy wiht the outcome. I had the advantage of spending as much time as I liked to get it as perfect as I could and satisfy myself. T
there is a pool table mechainc that thinks Im not authorized to advise and doesn't like reading anythign too long, thats ok.. he's made a few rude coments saying im not experienced anough to advise or things to that effect.. my take is the purpose of the foum is so forum members can share ideas, share info, and discuss experiences and things, help one another learn. It very old school thiking that giving out the secrets of your trade diminishes your trade but maybe some still think like that. anyway I don't claim to be any authority, and my only reason to write all this is to try to be helpful..
I don't see much that's very complex here, mostly just taking enough time to "get it right so you are happy," . True flatness and also true level is exacting and thus infinite so you can go to the point of rediculousness with super accurate machine setup levels if you desire to.
My take on it is this is something a reasonably thinking person can work through on their own although they may not do it as fast as a "pro" .. If you DIY, you can set your own thresholds on perfection. Personally I'd rather keep those decisions within my own control and wasn't worried about the time taken at all. It's different economics for a pool hall owner paying by the hour to come in and change all his cloth without interrupting business too long.