Surface Grinder refurb

Thanks Pete,

Just what I needed.

Andrew.

Double post again!

Edited By Andrew Tinsley on 02/10/2022 12:41:26

After realising quite how much effort it’s going to take to get this surface grinder scraped, on Sat morning I went out and got a cheap reciprocating saw, having watched a bunch of YouTube vids about making a poor man’s Biax scraper. I did it, and it worked quite well, for about 10 mins, at which point, what SpaceX would call “Rapid Unplanned Disassembly” occurred. I fixed it but it happened again.

Never mind. A lost day and a few £££. At least I tried. Back to hand scraping today.

I think your scraping is improving, it looks a more consistent on your last image. I hope I didn’t send you down that power scraper rabbit hole; I have been working on mine on and off for months, it’s Makita based as I can get parts for it relatively cheaply. The main issue is balance as the scraping gubbins is heavier that the saw blade & clamp. I have increased the counter weight but need to do more testing. It can produce a nice even pattern so I think it will at least  do for initial roughing. There is an alternative design on the Tube base on what looks like a windscreen wiper motor, the design is good but it’s more of a scratch build but I am tempted.

I think your lack of depth of scraping at least in part due to the sharpness of your blade. You also said you are having trouble aiming the blade; join the club, some put a sharpie mark down the centreline of the blade to help. I found it took me a few months until I started to get the hang of it, unlike a chisel where you have a wide contact, with the radius on the blade it’s tricky to get that centre on the desired spot. I would suggest slowing down, place the blade on the spot then look to see where you have placed the blade before making the scrape The difference between a hit and a miss is quite small.

Out of interest where are you based?

Edited By Tony Ray on 03/10/2022 00:42:55

One of the advantages of using hand/fingers to apply the oil-based blue is that you can sense the film thickness by the quality of the drag felt by the fingers. I'd imagine that, with a bit of practice, you could get a pretty even, thin film with your eyes shut. I've no experience of rollers or water-based media, so things might be easier, or at least different with them.

I assume you've come across the idea of pushing the scraper with your body, the handle having a suitably-shaped 'mushroom' load-spreading end. Most folk aren't strong enough to push hard enough, for long enough, with arms alone, on a job like your column's front face. For roughing, at least, where you need to hog off quite a bit of material, you can afford to, indeed need to, push downwards and forwards hard, creating deep furrows. It's hard work! This not only removes material, getting you towards the desired level, but it also breaks up the area of 'too high' material into smaller bits, which are than easier to scrape off.

Take heart - aiming is initially difficult, but it's a skill, and acquiring skills requires practice.

Sharpening has been mentioned. Different people have advocated different tip shapes. This suggests it's not critical, and, in any case, you will alter the contact geometry by the angle of attack you choose. The easiest way, I believe, is to hold the scraper vertically over the sharpening medium. Try to hold the handle's extreme end still between finger and thumb, fixed in space, but allow it to pivot, and then swing the blade sideways across the medium, from side to side (ie plane of swing is the plane of the blade). This will automagically produce a tip radius that is reasonably 'correct' for the handle length (but don't get too hung up on geometry). Carbide tips are wonderful, but the edge readily breaks down (in use and also when sharpening) into almost microscopic roughness, which causes scratches on the workpiece. A fine diamond plate works well, but not one of the 'perforated' ones - these can chip the edge. Check the edge with a 10X loupe.

Scraping an entire machine is a formidable task. As I get older, I'm increasingly aware that time is running out more quickly than is money (thanks to pensions...). My arthritic hands and wrists already limit some activities, and are only going to get worse, and I have a number of machines waiting to be restored. To hell with the expense - I feel a Biax coming on!

I had a couple of hours before work this morning, thought I’d have a good look at my blade. Under a magnifier it was clear that it wasn’t really sharp at all. Out of frustration I grabbed an old eclipse scraper I have to see how it performed. It was a total revelation. I found I can get it really sharp in about 15 secs with a simple diamond hone. And being short, I can get my elbow behind it. I was getting the little black piles of cast iron dust at the end of each scrape again. Sure it goes blunt after a pass or two, but it’s so quick to resharpen it isn’t a problem. Just goes to show that hi-tech carbide isn’t necessarily better.

I’m in Hitchin, near Stevenage.

Edited By Steve355 on 03/10/2022 11:48:44

That's interesting, I picked up a Makita one myself, specially for that attempt at a conversion, but haven't started yet, as I was struggling to come up with an easy way to vary the stroke length due to the internal design.
How did you address that?

Bill

Bill,

Mine's a Makita JR3050. I machined off the counterweight on the large bevel gear (it was pretty hard definitely a job for carbide) and machined a deeper counterweight incorporating a sliding dovetail which carries the crankpin. To accomodate the increase in height I have added some spacers between the two halves of the aluminium castings. The dovetail is locked with a couple of grub screws. I have to remove the a cover to adjust it. As designed radial play in the reciprocating shaft is limited by a crude bent metal U shape and the amount of play was unacceptable so I machined a sturdier block and fitted bronze wear strips and surface ground the 'ears' on the reciprocating shaft. I'll put some pics in my album this eve when I get home. As I said balance is the main issue meaning that it vibrates excessively. I intend to measure this and empirically add weight to the recip. shaft to see if it is reduced - if it is it means the counterweight mass is too high and I can reduce it, if not it means the counterweight is insufficient so I'll drill out some areas and fill the voids with lead. I'm using a PWM speed controller and the stroke length is limited to 20mm. I'm using the saw upside down compared to it normal use as the shape is better and I am working on a Biax like bulge to fit on the flat-ish area. I have ditch the Makita handle and intend to 3D print a shorter cover which will hold the speed controller. I am working on other projects so it hasn't had a lot of attention recently.

Tony, Thanks, I'll not hi-jack Steve's thread any further.
Bill

Steve,

The scraping with the Eclipse is showing nice high spots with the classic darker outlines but I would run into elbow issues with such a short handle, as has already been mentioned being able to put your body weight through the scraper is a real help in getting good scrapes and it takes some of the strain off the arms. Perhaps you can make a longer handle for it. Your sharpening method is clearly working for the HSS blade but is sub optimal for your carbide. The Sandvik carbide blade I have is excellent when sharpened on the rotary diamond lapping setup I described previously, only taking a few seconds to restore a a good edge and it holds up well. I have yet to work out how often I should sharpen it but as it’s so quick to do and it removes so little material it’s worth doing sooner rather than later.

I’m in Southampton.

Hi Tony

I think it’s because the scraper is shorter that I can get my weight above it and really dig in, whilst controlling the length of the stroke. And also, I can scrape kind of “backhand” with the back of my hand facing my face (probably makes no sense!) and that’s even easier than a forward scrape, and I don’t need to turn the workpiece. A picture would help explain. I have 2 carbide scrapers, one about 3 foot long from eBay which cost £60, and one I made myself, about 2 foot. I’ve barely used the expensive long one. The home made one is currently superseded by the Eclipse scraper.

For some reason my carbide sharpening hasn’t been working. But whilst the HSS blade needs sharpening more often, when it’s sharp, it’s very sharp.

Problem is, I don’t know anybody locally who is remotely interested in machining, scraping (or plane making and other things I do in my spare time). It’s a bit of a niche passtime!

Edited By Steve355 on 05/10/2022 09:55:28

The loneliness of the long distance scraper ...

I am lucky in that I have two friends quite close to me one is interested in scraping but hasn't done any and the other who has attended a Richard King course but whom I have yet to see scape anything. I first met one of them when he turned up to buy something I'd put up on Gumtree we are all interested in restoring / improving machines. Your plane making sounds interesting.

If you would like to PM me I'll give you my address and if you wanted to you could send me one of your carbide inserts and I'll put edges on it (assuming is not braised on to the scraper!) You would at least then know what a sharp carbide can do.

I can't see how a 3' scraper would work but I'm relatively new to this. I do recall as kid spending a lot of time in a neighbour's workshop; he had a few weird looking objects on the wall which he told me were scrapers and he briefly explained what scraping was. These tools looked a bit like upside down swan necked carving gouges with a bit of probably tool steel in the the end, I think with hindsight they were pull scrapers.

Yes a pick of your scraping technique would certainly help.

The easy way to guarantee a good honed edge on a scraper blade is get a coarse wheel (4-600) and grind the radius dead square on the end. Then switch to your edge sharpening wheel (I use 1500 normally) and very lightly put your negative rake edges on. Because the insert is first ground square you only need to grind very lightly each time you sharpen as the cutting edge needs only be half a thou wide and gets a little bit wider each time you sharpen. This will not only save your fine grit lapping disc but help you to avoid sharpening everything BUT the edge, a common problem with novice scrapers.

Testt he blade against your thumbnail. If it digs in with only the lightest of pressure it's sharp.

Progress….

I scraped the top of the table to about 12 points. There are a few areas that I’m not totally happy with but I could go on forever.

The sides are parallel to about .005 so I’m not messing around scraping those.

The sides are square in so far as I can’t get a 0.0005” feeler strip between the square and the metal

I’ve started on the bottom. If anything beats me, it will be this. They are quite worn going up at the ends by 0.003. Quite big patches of 0.002. I’ve tried scraping but it’s slow. I have tried a file as recommended by Pete but the two rails (?) are not evenly worn, and if I try to file just one side it’s very easy to end up with a hump in the middle and low at the edges. Ideally I’d fly cut it on a great big mill but obviously I don’t have a mill big enough. My surface plate isn’t quite big enough, but will probably work ok.

It is hard to measure. I’ve tried using a gauge block, perhaps that will help.

I have a feeling that this is going to be very very time-consuming and hard work.

I’ve also been looking at some gibs. They don’t seem to be worn (consistent micrometre measurement along the length), but they are warped, with a hump in the middle of a few thou,

Albeit on a shorter table, so less overall area to scrape off, but mine were something like 12 thou high at one end and 14 at the other, so I ended up taking nearly 15 thou off each end and one thou in the centre.
This was where I found myself taking a long time, due to trying to save money using a variety of lumps of carbide, all of which were all the wrong grade.
Tough yes, but unable to take, or maintain a very sharp edge.

It was also during the first lockdown, so obtaining stuff was a bit more difficult.

Are you using the correct grade of carbide yourself?

Bill

It’s the carbide that came with the scraper. I haven’t had a lot of success with it. I actually prefer my old Eclipse HSS scraper - it’s a better length for me and is dead easy to sharpen, and when sharp it seems to hog off quite a lot of cast iron.

I had an idea to try to use my little horizontal mill for it. It’s far too small for the surface grinder table but I only need to skim a couple of thou off the ends. If I’m careful I can probably do it, I will give it a go tomorrow.

Re the gibs, as I see it you have 3 options:

1. Leave them as they are but stone off any high spots. If the gibs are adjusted by a series of screws they will largely take out the bend anyway.

2. Try to take out or reduce the bends, if it’s just one bend per gib this should be straightforward; your woodworking vice will easily have enough power to do this. Follow this up with scraping for oil retention.

3. Make new ones, ground flat stock can save a lot of work, don’t forget that once the grinder is running it can be used to make parts for itself. The short one would be easy to reproduce.

Right now your table wear is the thing needing your attention, you can always come back to the gibs at a later date.

Ref the table.

Let me express my concerns first; you are trying to bring a surface into flatness that is that is larger than your surface plate, this is where a suitable straight edge comes into its own. I can’t remember what length you are getting from Lamb’s if it’s not scraped in and longer than your table you’ll face the same difficulties.

The top surface is now flat to your satisfaction, this is your reference surface which should be used whatever metal removal process is employed, here are my thoughts:

Put the job out to an engineering company to take the bulk of the material off the flat ways, It might not be as expensive as you think.

Find someone with a larger mill ( not clapped out) to help you with it.

Use your mill, but be realistic, how flat is its table? Can it support the weight of the grinder, dangling the job off the end even on Bridgeport will affect the depth of cut etc.

Finally a radical idea: mount a bench grinder to a flat sled / base with 3 points of contact that rides on the surface plate and grind the material off. I would hinge the grinder on one side and adjust the height using an elevating screw. Like a router cutter the grinding wheel only has one point of contact and once dressed will be co planar with the plate I think I saw NY CNC do this to a straight edge prior to scraping. I would probably only do this on the flats. I would use a 46 grit surface grinding wheel which you will need to bush to fit the grinder. The elevating screw at a fine pitch will give you good control. To be clear you move the grinder sled not the job.

Ok another idea, look up Gena Bazarko on the tube he’s Russian but he shows using a Demel or similar to put ‘scrape’ marks on a straight edge, He follows the 45 degree system just as one would with a scraper.

Whichever you do I would do the dovetails by hand as you will have more control.

Tony

Beware of apparently bent gibs. They can bend a surprising amount due to uneven temperature through them. I had a pair of gibs for the shaper seem to have well over half a thou of bend and I scraped it out. Next day the bend was the other way... I realised that they had had a day for the temperature to normalse.

After that I kept them chocked up so that air could circulate around them and used a fan to make sure that it did when I wasn't working on them. No more issues with gibs flapping about.

Hi Tony

What I tried to do was to use my Burke horizontal mill to skim the last quarter or so of the bed. The wear was all in the middle, so skimming those sections bright the ends in. It wasn’t altogether unsuccessful. In general, there’s about 0.001 of variation now, a little more in places.. The extremities were a lot more difficult to do, so one is high and one is low. The high one can be scraped, and the low extremity probably doesn’t really matter.

However, I am very tempted to do as you suggest and see if a local machine shop will do it. They should be able to get it all much flatter that I can prior to scraping. I will ring around on Monday and see what I can find, as you say it’s a simple and quick job for someone with a decent mill.

Re the surface plate, diagonally it is about 2 inch shorter than the full length of the table. This is by far the longest surface on the grinder, and I just couldn’t justify or afford (or move) a bigger plate. But if the table bed is pretty flat (say 0.001) before it is spotted, well I haven’t done the trigonometry but the potential error (1 thou in 32 inches) is incredibly small.

The straight edge that’s coming is sized for the dovetails, so it’s 24 inches long which is the length of the longest dovetail. I don’t think a bigger straight edge would be easy to handle.

I think you are right about the gibs, given they don’t seem to be worn, just slightly warped, they should be fine. As Mark suggested, they seem to have improved since I took them off the machine.

I understand your constraints regarding the surface plate, although as you say the potential area will be small the difference between a high spot and a low is also incredibly small. It will be worth researching what others have done when faced with a similar situation as there are techniques that can be used to minimise any error.

I would ask any shop what tolerance they can hold over the length of your surface and I would be looking for precision engineers; you can tell a lot by the cleanliness of their premises if you visit them.