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[The_kindred_soul]

Hi everyone, new member and first time poster here!

I recently acquired a bunch of old Mercury lapidary equipment for my wife. We set up the slab saw today and noticed some oddities that we are trying to find some answers for.

On this particular model, the sled track is set at an angle away from the blade, no more than a couple of degrees. The sled itself has its rollers set up in such a way that the sled stays parallel to the blade but at the end of its track it's about 1/8 of an inch away from the blade.

Am I missing setting here or is this supposed to be how these things function? To me, logically the rock should travel completely parallel to the blade without moving away. Which is evident as there is obvious tear out once the blade nears the end of the piece being cut.

Thanks!

[vitzitziltecpatl]

Welcome!

You're right that the carriage travel should be parallel to the blade.

You might be able to adjust the blade if there isn't any (or enough) adjustment built into the rail mounts.

[The_kindred_soul]

There is very tiny amounts of play in the carriage, mostly just adjusting within the holes. The arbour does not look to be adjustable, unless its shimmed a bit, and even then would require widening of the slot in the deck. My idea right now is to just widen all the holes on the carriage and track a couple mm, hopefully that will allow enough play in the setup that I can square things up that way. Alternatively I would put the carriage on the drill press and punch 2 new holes for the rollers that are more square than the originals.

Other than that, these are very heavy 50+ year old pieces of equipment that seem to be solidly made, most pieces look to be made from cast iron. I'll try the widening first and see how that works.

Look forward to posting some photos of our work!

[peruano]

Photos of the saw would be desirable as well.  I have an 8" Mercury trim saw; it does have a sliding vice which I do not use often.  IIRC Mercury products were made in Edmonton, Canada.  I have not read or seen a lot about them.  If your deviation is not corrected by your minor adjustments, it may be tolerable since the rock is moving away from the blade and not crowding in to it.  Does your vice move on rails, or is it guided by the rim of the saw table?

[55fossil]

       If the angle of the blade is off you get the same problem with the bed being out of line front to back. So you might look for a way to adjust the arbor that holds the saw blade. A very tiny amount of angle change makes a huge difference in a large saw blade front to back.

   While it is sometimes necessary to modify old saws, this saw did run true at one time. Almost all saws have a way to adjust the saw blade arbor. Also, on my old Frantom, the whole carriage can be loosened or removed. There are bolts to the carriage that when loosened allow a small amount of adjustment but that is not what they are for.  good luck

[The_kindred_soul]

This afternoon I managed to modify the carriage track with bigger holes and she now runs true to the blade at the leading and trailing edge. At least as true as I can get with a tape measure and eye balls.

I also strapped on a new Princess auto diamond blade. Not stellar quality as the blade seems to be a touch unbalanced. That being said, she cuts much better than before. We are still finding that the final few mm of the cut tends to either blow out or completely shear off. Which is irritating but not a complete deal breaker yet.

Some photos of the saw and some cuts are attached. The saw is working well enough that tomorrow I'll be working on the polishing station, and\or the lap wheel.

[peruano]

If I am interpreting your photos correctly, you are probably using gravity feed, and if so the blowout at the end of the cut is totally to be expected.  Some folks try to avoid this by having the weight driving the system arrive to a water container that effectively lightens the weight and reduces the pressure of the rock to make the last few mm cut slow and reduce the beakout risk.  Or merely disconnect the weight and finish the cut with hand pressure. 
You have not stated how big your saw is.  10" or larger?  Gravity fed saws are a fine art and practice makes perfect.  Slow is best even though it may be frustrating to wait.  Good luck; you are making some nice slabs. 

[vitzitziltecpatl]

Yep - what Peruano said. I've used a small box with layers of low-density foam beneath the weight to slow the cut at the end.

[The_kindred_soul]

Yes that's definitely a gravity fed system with lead cast into sardine cans as weight. Crude but it works.

Thanks for the suggestions,  I'll try some of those ideas later and see which works the best. We have already experienced what happens when the fees rate is too high, that carriage being attached at one end allows for a lot of bouncing on the blade if pushed too quick.

Yes that's a 10 inch saw, the largest piece we put thru yesterday took almost 15 mins, which from what I understand is a normal amount of time. I did have other photos of the saw to post but apparently they're too big and i was working nights and didn't have a chance to figure out how to shrink them. I'll try that later on today.

Thanks for the compliments, stay tuned for more!

*** Side note - is there anyone in the central Ontario region who has a large slab saw available for rent? I have 2 rather large sodalite boulders I'd like to slab up and some smaller amethyst chunks my wife wants sliced vertically.***

[peruano]

Are those saw marks that diagonal across the first slab pictured.  If so, they suggest a stop/start movement or a surging (perhaps feeding too fast) for the cutting efficiency of the blade/rock combination.  If so, I'd suggest an even slower feed rate (lighter weight) to produce the smoothest slabs you can possibly produce.  My slab saws with power feed run on the average of 7 min per inch.  I know thats frustratingly slow but thats rock work.  Build yourself a hood, and devise a schedule of grinding rocks while the saw runs gently into the rock and you will have a winning shop.  Find someone coming to New Mexico for the winter and tuck the sodalite in their trunk when they are not watching.   

[The_kindred_soul]

Yes those are definitely stop and start marks. My wife is impatient and wanted to cut it open as fast as possible 

I keep reminding her that slow is fast. I'll have to show her your post hahha. We did have a heavy weight initially and it caused the rock to bounce like crazy on the blade. I'll try another rock today on the small weight.

Once I get the lap wheel going we will get them smoothed out, it'll just take more effort.

[peruano]

Here is my saw with the vice apparatus sitting in place but not officially attached.   It occurs to me that if your vice is like mine it is guided by a bar attached to the side of the saw table.  If that bar is bent or not firmly seated it could cause and alighnment problem. 

[peruano]

Apologies for the sideways photo.  The gremlins did it. 

[The_kindred_soul]

The issue I'm finding now is with the carriage flopping at the blade end the rock also tends to bounce on the saw blade. The last piece I cut yesterday I ended up slipping my hands under the shield and physically putting down pressure on the threaded rods, and that definitely improved the cut speed and accuracy.

So now I'm considering adding a track that sits above the carriage and restricts vertical movement of the specimen. I mean I hate to modify it a whole lot, but less weight still caused it to bounce on the blade. At the end of the day though, it was a good bargain at the time. If I have to add $20 in modifications then I'm still better off than buying a new machine. For now at least ...

[vitzitziltecpatl]

Our old HP 10" has a u-shaped rod (90 degree corners) with a roller bearing on one end to keep the carriage down.

It is mounted into a hole on the carriage, and the roller bearing is up against the bottom of the saw table. Works quite well.

Don't know if you could add something like that to your saw or not, but it's a thought.

[The_kindred_soul]

That is a genius idea. Much better than tapping holes in the deck with some contraption that needs constant adjustment. I'll definitely look further into that one, thanks!