Choosing flat lap disks - type and grit

[seachange]

Hi,

Could I please have your help with choosing some flat lap disks? 16", no hole, magnetic backing. Using a converted pottery wheel.

Main use will be grinding the edges of some 3 to 9 mm ( 1/8” to 3/8”) thick bowls. Horizontally, parallel to the base. Would like to achieve a “gallery quality” finish on the bowls. Imagine that some bowls will be ok with a matte finish, but some will need a polished border.

Have a convington wet belt sander for vertical borders, but think I need a flat lap for horizontal borders...is this correct?

Have looked at His videos, read the flat lap and polishing sections in J Schmuck book, and as much as I could find here. My head is just whirling with information.

Still confused if I need diamond 60, 140, 270, 500 (which gets rather expensive, specially since I am new to making larger items and don't know what the future holds in respect to selling them successfully).

Also confused re use of smoothing disks compared with diamond.

The smoothing disks are cheaper, though not as long lasting. But I still don’t quite understand if they replace diamond disks, or fit somehow in between the sequence of diamond grits. Is anyone here using them?

Since this is a completely new project for me, with unknown results, would it make sense to start with a sequence of diamond 140 and 270, then something on float by hand (pumice? which grit?) to get to the equivalent of 400 grit, then felt with cerium for final high polish?
This would be a purchase of 2 diamond disks and one felt. The felt disk for the final cerium polish is reasonably priced...at least when compared with the price for the diamond ones.

Or do I need to get somehow to equivalent of 600 grit before felt and cerium?

Is 140 grit enough to start with to get flat horizontal border or should I use 100 grit? Or 80 grit? The lower grits are quite a bit more expensive, but the disks are going to last me a long time, no savings if I buy the wrong ones.

I will contact His, but would love to hear from the experience of this board members before I do.

This is a big thing for me. A big step from jewelry making, a big step into the unknown business wise, a big challenge technically…and big fun. Well, I am sure it will be big fun when this is solved, feels somewhat like a headache at the moment.

Many thanks in advance. I am really looking forward to sorting this out, placing the order and moving on with these projects. Have been dreaming about this for a long time

All best wishes, seachange

[David Jenkins]

I found the His Glassworks material to be very helpful.

I wouldn't get a 60 grit disk until you know that you really need it. It's very aggressive, and you'll probably find that it produces some chipping where it can't be tolerated. I have one that I got with my initial inventory of disks, and after a couple of attempts to use it to even up some bowl edges, I never use it anymore. JMHO

[Morganica]

Flat laps are useful for evening out a surface to exactly the same plane, such as making the edges of a bowl parallel, flattening the usually convex surface of a full fuse, or flattening the base of something to make it stable.

I started out with 220-400-600, then cork for polish. Worked well--I've added other disks over the years to do different things, or improve surface quality.

I use a 60- or 100-grit disk for very rough shaping, often of sculpture. They remove a lot of material, very fast, but are rough on the glass. They tend to chip out edges, as David said (although putting a slight bevel on the edges first prevents a great deal of that), so I generally switch to 220/270 before I've gotten down to the level I want. The 220 is my main disc--it does the final shaping. If I tried to chew off a lot of glass with a 220, I would be grinding much, much longer. I use 400- and 600-grit discs to refine the surface.

Smoothing discs don't replace these discs, they are for prepolishing and removing grinder marks, or sometimes polishing depending on the finish you want. I find even the 600-grit surface to be a bit rough with diamond and will use the smoothing discs to get a really silky surface that is much faster to polish to a high shine. Not everybody uses them, you can get a good surface without them.

Jonathan Schmuck's book is extremely useful, if you have a copy. The best resource, though, is probably HIS. Call them, tell them what you're doing, and they are usually pretty good at steering you away from stuff you don't need yet.

[The Hobbyist]

I've been getting excellent results using grit. I have a rociprolap that I use to grind down the edge. I am usually super aggressive (with chipping) at 30 or 60 grit then I move to 220 - 320 and then finish with 600. I use a pad and cerium oxide to polish. Both machines are 24" diameter.

The most difficult part of the process is cleaning the rociprolap between grits, it's heavy. I'm getting it down to an acceptible routine though. The cerium polish is effective but boring.

I have put a knife edge on bowls with no problem, except cutting myself.

Jim

[seachange]

Hi David, hi Morganica

Many thanks for all your input, great information...I just couldn't sort it out by myself

Will email His straight away.

All best wishes, seachange

[seachange]

I've been getting excellent results using grit. I have a rociprolap that I use to grind down the edge. I am usually super aggressive (with chipping) at 30 or 60 grit then I move to 220 - 320 and then finish with 600. I use a pad and cerium oxide to polish. Both machines are 24" diameter.

The most difficult part of the process is cleaning the rociprolap between grits, it's heavy. I'm getting it down to an acceptible routine though. The cerium polish is effective but boring.

I have put a knife edge on bowls with no problem, except cutting myself.

Jim

Hi Jim, many thanks for your reply. Have thought long and hard at the possibility to use only grits. But at present I feel it will add another level of inconvenience for us. At present all my equipment is in storage, don't have a wet studio yet. So each time I use it we have to drag it out onto the paddock, then at the end of the day clean and dry everything to store it again.

It surely is better than nothing, but not ideal. I feel I'd like the ease (less mess, less cleaning) of diamonds, so the whole thing does not become too work intensive.

We are planning a wet studio for next year, but this is a while to go. It is all right, being 'not young', I don't want the time to pass too quickly

All the best, seachange

[Morganica]

Actually, you can do a pretty good job with just grit, cerium, a little water and a sheet of float glass and it takes less time than you'd think. Plus, it's an excellent solution for studio space problems.

[David Jenkins]

I wholeheartedly second what Cynthia says: We did a lot of grinding in a class I took recently at Hot Glass Houston, and I was amazed at how fast it went. We used three or 4 progressively finer grits, and each took just a few minutes. Cleanup was not all that hard. Only [minor] downside was that it's a fairly noisy process.

Inexpensive, quick, effective, and easy. (Sounds like a commercial for some sort of personal health product, doesn't it? )

[seachange]

Many thanks Morganica and David, that commercial is almost convincing

The part I never quite understand is if this works for the polishing end of the work, let's say from 400 grit upwards, or if it is also "quick, effective, and easy" at the beginning of the grinding, the 'shaping stage'...you can see from my wording that I have been reading my J. Schmuck

Let's say I have slumped my 1/4" thick disk into the mold. Now I have a bowl and the perimeter has the rounded edges of the original blank. Have to grind away at those edges until they are flat and parallel to the bottom of the bowl .

Can I achieve this, let's say within one to two hours, by hand with grit on float? Assume the grit would have to be rather coarse.

I mention one/two hours because after the shaping I have to go through all the other grits to get a nice 'see-through the edge' type of polish...it is winter, the days are short

The reality is that if this works in a reasonable time, it would be a wonderful solution until we have a better working space. Plus at present, I am only planning to make a few of these bowls.

Longing to know...many thanks!

Seachange

[Morganica]

Depends on what you started with (did you edge the blank before you started the slump, did it slump evenly, etc.), your technique and speed, the size of the grit you're using, how much material you're removing and how tight you want the polish. If you've got to remove a half inch of really jagged material with 270 grit, you're going to be there awhile.

Honestly? If you're working with a raw, just-fused blank edge it will most likely take longer than a couple of hours to handlap it down. OTOH, until you're practiced, achieving a perfectly flat and even, transparent, high-gloss polish on a bowl edge using a flat lap will take longer than an hour or two anyway. It ain't as easy as it looks, and at the speeds the flat lap is traveling, the bowl can get away from you and smash, especially if you're trying to freehand it. I still have the scars from my first bowl explosion.

One other advantage to hand-lapping: You can set up in front of the TV pretty easily, pop in a video or two and grind away, sorta like knitting. Pretty tough to do that with a flat lap.

I cheat--I pre-edge my banks at an angle before I slump them, which can be done quickly (i.e., in less than an hour) on just about anything, including hand-lapping. If I want a shiny, transparent edge I take the edges to 600 grit, then stick them in the mold and slump, going just a little hotter and longer than is strictly necessary. The glass fire-polishes along with the slump, the edges face up, not out, and it saves me a heckuva lot of time and elbow grease. Plus, if the bowl slumps unevenly I've left myself a lot less coldwork at the finish (unless it's REALLY uneven, in which case I decide that what I was really after was an asymmetrical bowl).

It doesn't always give me a perfectly flat and parallel edge, but it's pretty close (and again, if I need it perfectly flat it's already most of the way there so it goes pretty fast). One big advantage: Fused glass frequently has little bubbles just below the surface that turn into pinholes in your finished edge. Firepolishing won't get rid of the big divots, but it will seal over the smaller ones.

I'm not sure I'd spend a couple thousand bucks on a flat lap and diamond discs if all I needed was to flat-edge a few bowls. And the nice thing is, it's easy (and cheap) to give it a shot. You can always buy the flat lap if it doesn't work. (If I were you I'd get a copy of Paul Tarlow's book, "Coldworking without Machines," first thing.)

You can buy enough grit for a year--60-100-220-400-600--for about $40. The same amount of cerium will cost $50-60, and you'll need a bucket and a measuring cup from the kitchen. The glass base is usually free--you just need a 1/4-inch or thicker piece of float that's at least 2x the diameter of your bowl. At some point you'll wear a depression in the float, so turn it over and use the other side. When that side's messed up, cut it up, throw it in the kiln and make bowls out of it, get yourself a new base.

[Stephen Richard]

......

I cheat--I pre-edge my banks at an angle before I slump them, which can be done quickly (i.e., in less than an hour) on just about anything, including hand-lapping. If I want a shiny, transparent edge I take the edges to 600 grit, then stick them in the mold and slump, going just a little hotter and longer than is strictly necessary. The glass fire-polishes along with the slump, the edges face up, not out, and it saves me a heckuva lot of time and elbow grease. Plus, if the bowl slumps unevenly I've left myself a lot less coldwork at the finish (unless it's REALLY uneven, in which case I decide that what I was really after was an asymmetrical bowl).

It doesn't always give me a perfectly flat and parallel edge, but it's pretty close (and again, if I need it perfectly flat it's already most of the way there so it goes pretty fast). One big advantage: Fused glass frequently has little bubbles just below the surface that turn into pinholes in your finished edge. Firepolishing won't get rid of the big divots, but it will seal over the smaller ones.
............

Just to make sure I understand. You take the flat fused piece and put an angle on it (?30 degrees or so? - I can't find the Spanish upside down question mark). This will be from the bottom edge toward the top, yes? Do you leave a bit of a lip on the bottom edge, or make that relatively sharp. I guess I am asking how much rounding of the bottom edge can be achieved in a slightly hotter, and longer soak.

If you are doing this by hand lapping, the angle won't be exactly the same all the way around, but perhaps that does not matter.

I'm asking all these questions because it seems to me a better alternative than what I have been doing.

Thanks for your inspiration and help.

[Haydo]

I'm in the process of aquiring a Venco flat bed grinder and will probably let the supplier get me a 120 ish disc just so I can hook into all the trueing up needed to be done. Later when things settle I'll most likely see what Jon Firth from Unicorn Glass in Darwin can do for me. He gets belts and discs made to order with a 3 week wait, so I imagine there is a Sampan involved. - haydo

[David Jenkins]

I'll amend my previous post to add that the bowls we were working with had been dropped through a Ceramaguard (sp?) board and the "flaps" had been sawn off. The resulting bowl edges were already semi-flat, semi-smooth, and semi-parallel before we started hand grinding. (Please - no math majors' comments about 'semi-parallel'.) So we probably spent no more than 10 minutes or so at any given grit.

It's kind of a mindless activity. Tranquil, almost. You can talk to your neighbor, watch old Seinfelds, ... whatever. Not at all onerous, IMO.

[Morganica]

Just to make sure I understand. You take the flat fused piece and put an angle on it (?30 degrees or so? - I can't find the Spanish upside down question mark). This will be from the bottom edge toward the top, yes? Do you leave a bit of a lip on the bottom edge, or make that relatively sharp. I guess I am asking how much rounding of the bottom edge can be achieved in a slightly hotter, and longer soak.

If you are doing this by hand lapping, the angle won't be exactly the same all the way around, but perhaps that does not matter.

I'm asking all these questions because it seems to me a better alternative than what I have been doing.

Thanks for your inspiration and help.

The angle depends on the mold I'm using--I have a contour gauge that I set at right angles to the table, take a profile off a bowl made in that mold. Then I run a tangent off the profile and figure out where 90 degrees parallel to the blank and 90 degrees parallel to the table would be. The difference between those is the angle I use on the grinder, or maybe a scoootch less. I used to cut a jig (just a wooden block big enough to hold the blank at the right angle), fasten it to the edge of the flatlap and then just rotate the blank on the jig. I had to check it frequently to make sure not to break through the corner of the opposite edge. It works with hand-lapping too, although it's really messy. Once I have the jig I can use it repeatedly if I'm careful with the grinding. Be interesting to see if you could steal the concept of the faceting wheel's control arm and use that to get a very precise angle that was repeatable and also adjustable...dunno.

Anyway, like I said, it isn't exact but it can get surprisingly close if I can control the slump. I usually cut a second bevel to break the edge of what will become the outside corner edge of the bowl--that helps conceal any flaws. The big deal is that you get your edge all or partway there, and it's much much easier to true it up, put it back in the mold and firepolish the edge if you need to.

[seachange]

The angle depends on the mold I'm using--I have a contour gauge that I set at right angles to the table, take a profile off a bowl made in that mold. Then I run a tangent off the profile and figure out where 90 degrees parallel to the blank and 90 degrees parallel to the table would be. The difference between those is the angle I use on the grinder, or maybe a scoootch less. I used to cut a jig (just a wooden block big enough to hold the blank at the right angle), fasten it to the edge of the flatlap and then just rotate the blank on the jig. I had to check it frequently to make sure not to break through the corner of the opposite edge. It works with hand-lapping too, although it's really messy. Once I have the jig I can use it repeatedly if I'm careful with the grinding. Be interesting to see if you could steal the concept of the faceting wheel's control arm and use that to get a very precise angle that was repeatable and also adjustable...dunno.

Anyway, like I said, it isn't exact but it can get surprisingly close if I can control the slump. I usually cut a second bevel to break the edge of what will become the outside corner edge of the bowl--that helps conceal any flaws. The big deal is that you get your edge all or partway there, and it's much much easier to true it up, put it back in the mold and firepolish the edge if you need to.

Aha, now I get it . This will give a good head start to the hand lapping. It will need some practice to hold the plate at the correct angle all around, but everything takes practice.

Morganica, many thanks for sharing your experience and for your advice. I will get the grits and try by hand. Had already ordered Paul Tarlow's book...just in case. Now I am very glad it is already on the way.

Taking it all together, my level of experience in making larger pieces (low), the cost of discs (high) and currently the hassle (also high) of moving the machine in and out of storage each time, this will be the best option to start with. As you say, I can always order the discs later.

I deeply appreciate the time you and others put in to condense years of experience into a few lines and create this aha moments for many of us. I wouldn't have a 'glass life' at all without this help.

Many thanks again and best regards, seachange.

[seachange]

I'll amend my previous post to add that the bowls we were working with had been dropped through a Ceramaguard (sp?) board and the "flaps" had been sawn off. The resulting bowl edges were already semi-flat, semi-smooth, and semi-parallel before we started hand grinding. (Please - no math majors' comments about 'semi-parallel'.) So we probably sent no more than 10 minutes or so at any given grit.

It's kind of a mindless activity. Tranquil, almost. You can talk to your neighbor, watch old Seinfelds, ... whatever. Not at all onerous, IMO.

Hi David, many thanks for replying and for clarifying the starting point. The devil is really in the detail

Starting from a semi flat surface has to make a considerable difference to the total time and labour. We go to the gym twice a week for a couple of hours each time...enough of a workout for me

All best wishes, seachange

[seachange]

Hi Stephen

Many thanks for posting that question. I was thinking how to formulate it, and there you were

All the best, seachange

[Stephen Richard]

Thanks Cynthia.
Now to try it out.