my take on a slow speed lap

[mtraven]

My primary project involves scraping, actually making a power scraper, but ya’ll keep telling me I need a lap. So I finally built one, entirely from scrap laying around the shop. Zero planning, dirty build, but she spins nice & true @ ~260rpm which ever direction you start her.


Took a lot from both Stephan & Dale’s videos on the subject. If you're building one, I highly recommend checking those out. A few notable improvements I thought I’d share:

the table (borrowed from another grinder) has a different trunion system that keeps the front edge a constant distance from the wheel at all (practical) angles. Pretty nice feature, I think. But that creates a new problem, how to get the wheels off? I’m built this to try the diamond bonded steel plates. 6" OD, mount on a 1/2" center reg, have (2) drive pins & a ring of (3) & (6) 6mm neoD magnets. That setup needs ~0.100” of clearance to be removed. But I also wanted to leave open the possibility of a cast iron lap that I’d charge with diamond. That requires a lot more clearance.

I could just move the trunion to its extreme, where the table gap opens up. But then I am resetting the table angle in between grits—I don’t like that. After lots of starring & fiddling I came up with this secondary pivot system that rolls the whole bed back & drops an edge, tangent to two pads, forming a repeatable hard stop. The whole thing locks down with ~2 turns of the thumb screw-which need only be loosened(not removed completely) to retract the table.

[mtraven]

here the backer, mounts on a 60deg taper with (6) 8-32 countersunk bolts. Magnets are epoxied into pockets, slightly sub surface to reduce the magnets pull. Pocket filled flush with epoxy so to not create a pocket for fillings to build up (ask me how I know).

[Doozer]

LOVE THIS.
It is basically a high power low speed Glendo AccuFinish.
I took my Glendo apart and it has a motor like a box fan,
the kind you put in a window or otherwise. A shaded pole
low torque motor. It works though. I would say it spins
300 rpm at the wheel.

-Doozer

[Peter.]

That's great, very similar in concept to mine except I tilt the disc.
Loads of people overestimate the power and rigidity required. Mine is adapted from a commercial item which has a shaft secured in a single ball race bearing which itself is just pressed into a plastic housing. Its driven by a very small open frame motor about 2.5" cubed with a large o-ring for a drive belt.

[BCRider]

Sweet project! I really like your solution for the tip away table that keeps it's adjustments.

I've been thinking of a similar low speed polishing tool using the same low cost discs. And I've got a very similar small size motor. I was also looking at some smaller section V belts as used on sewing machines. They are the toothed style that can fit around small diameter pulleys with better contact and would be a natural for this sort of light duty use.

[mtraven]

Sweet project! I really like your solution for the tip away table that keeps it's adjustments.

I've been thinking of a similar low speed polishing tool using the same low cost discs. And I've got a very similar small size motor. I was also looking at some smaller section V belts as used on sewing machines. They are the toothed style that can fit around small diameter pulleys with better contact and would be a natural for this sort of light duty use.

thank you. Its worth noting, I established the table to spindle position without the table retraction mechanism, I was real concerned about the table being parallel. Once I was happy with the position, I built the hinge, stops & lock, then cut the tacks that were holding the fixed table position. This ensured that even if my pivots weren't quite perfect(which their not), they would still repeat to grinding position.

re: belts: I wanted something smaller, lighter & more flexible, the 3/8 v was the closest I could find(@farm & fleet 😀 ), but it really should have more tension than I'm willing to pull on the motor shaft. Sewing machine belts are a good idea, hadn't thought of that. Curious what you mean by toothed belt? Is that a timing / cogged belt? or is the vbelt with groves on the tapered sides to grab the pulley better? Either one would probably be better, although I can stall that motor by holding the disc, which tells me I'm delivering all the power with that belt. And if I were to stall the motor during actual grinding, I've done something horribly, horribly wrong.

you might consider running gt2 / gt3 timing pulleys & belts. They are cheap & readily available from the diy 3d printer community. You could probably make the whole package a little smaller with those too. i think thats the way I'd go if I had actually planned this project.

[mtraven]

That's great, very similar in concept to mine except I tilt the disc.
Loads of people overestimate the power and rigidity required. Mine is adapted from a commercial item which has a shaft secured in a single ball race bearing which itself is just pressed into a plastic housing. Its driven by a very small open frame motor about 2.5" cubed with a large o-ring for a drive belt.

you don't have a picture of that do you? My original thought was to do just that, I couldn't figure out a way to deal with the belt & pulley attached to the disk. Unless your tilting the whole drive train?

[Peter.]

you don't have a picture of that do you? My original thought was to do just that, I couldn't figure out a way to deal with the belt & pulley attached to the disk. Unless your tilting the whole drive train?

Here is the machine. It was a tool for grinding planer blades (home shop quality). I drew up a mount in cad and my friend cut it out on his plasma table. I bent it up and mounted the whole machine onto the mount.






Here's the drive system inside the unit

[J Tiers]

You will like it. I have a Glendo, probably older than Doozer's, and it is very handy. I have 3 or 4 diamond wheels of different grit size. Yes, good for carbide, of course. But it also is good on HSS. The water used with it keeps any worry about overheating from being an issue.

Glendo sells a grinding fluid, but I've always just used tap water with a little soap in it to break the surface tension so it "wets" the wheel. A spritz on the wheel is good for long enough to touch up most things. And you can always give it another spritz if needed.

The Glendo has a nice sliding carriage, but yours has a slot for a sliding holder, which would work just as well.

[Mcgyver]

nice build, but why so slow? Are you not using carbide scrapers? If so, speed it up to grinding wheel speed or you'll be there for ever. There is nothing about diamond on carbide that won't work perfectly at 3 or 4 thousand rpm. The only reason I see for for slow like the Glendo is sharping steel with diamond or sharping carbon steel and not wanting to draw the temper

[Jim Stewart]

Huh. My take on a slow speed lap is around 2:45 at Sears Point.

https://www.sonomaraceway.com/

[mtraven]

Here is the machine. It was a tool for grinding planer blades (home shop quality). I drew up a mount in cad and my friend cut it out on his plasma table. I bent it up and mounted the whole machine onto the mount.

Here's the drive system inside the unit

still not sure I understand how it the disk tilts, but I dig that unit, particularly how compact a fit you got out of that motor & pulley. well done & thanks for sharing!

[mtraven]

You will like it. I have a Glendo, probably older than Doozer's, and it is very handy. I have 3 or 4 diamond wheels of different grit size. Yes, good for carbide, of course. But it also is good on HSS. The water used with it keeps any worry about overheating from being an issue.

Glendo sells a grinding fluid, but I've always just used tap water with a little soap in it to break the surface tension so it "wets" the wheel. A spritz on the wheel is good for long enough to touch up most things. And you can always give it another spritz if needed.

The Glendo has a nice sliding carriage, but yours has a slot for a sliding holder, which would work just as well.

ahh, I'm just getting ready to test it out & starting thinking about lubricates. I have heard the soap & water, also heard windex & w40. I'm inclided to try the wd40 first as its not gonna rust anything.

I saw the linear rail on a glendo, hadn't really put it together what that was for, thanks. I'll bet that linear rail feels a little better than my t slot, but you're right, it works.

[mtraven]

nice build, but why so slow? Are you not using carbide scrapers? If so, speed it up to grinding wheel speed or you'll be there for ever. There is nothing about diamond on carbide that won't work perfectly at 3 or 4 thousand rpm. The only reason I see for for slow like the Glendo is sharping steel with diamond or sharping carbon steel and not wanting to draw the temper

lol I didn't even read the name of the post & I knew it was from you, Mac.

Honestly, you're the only one I've had recommend high speed. although I do think you're right. The only potential flaw in your reasoning might be the bond between the diamond & the steel plate. But really I couldn't get past the fact the the people I've learned scraping from, use slow speed laps. Felt kind of arrogant of me to think I knew better. I think the reason we see low speed grinders is largely because they are repurposed from woodworking grinding, mostly HSS. and you explained well why its better for that. The other reasons I considered, is that it would be more forgiving to an untrained hand & facial runout might be easier to manage. my runout is < 1 thou, so I'm not worried about that, but I've never used a wheel like this and I figured slower speed was less likely to get me into trouble.

all that being said, your advice was not lost on me. You'll notice the spindle & drivetrain are distinctly separate. I can easily swap out the 1" & 6" pulleys for a pair of 3" & be running at 1750. I probably even have enough motor to overdrive the spindle @ 2-3k. As soon as I feel comfortable on the new machine, I'll start making those changes.

[mtraven]

Huh. My take on a slow speed lap is around 2:45 at Sears Point.

https://www.sonomaraceway.com/

lol you have no idea how many of those search results I had to sift through.