My Tool Grinder.

[BaronJ]

Hi Guys,
I started talking about making a tool grinder in another thread so I thought it would be better to start a new one rather than clutter up someone else's.

I have been collecting various bits and pieces for a while now. But the other day I got to weld the motor mounting plate to the base plate.

Because the motor is a salvaged 1200 watt universal motor from an old rotary lawn mower and runs at a terrific speed I need to slow it down somewhat. So I've also built a triac speed controller that I can use to vary the speed from a standstill to the maximum rpm.

The abrasive disc that I have acquired is rated at 5200 rpm so running it beyond that speed would be dangerous.

The photos show the various bits that I have completed so far. The motor mounting plate is 6 mm steel plate. I used a standard IEC socket and illuminated switch to supply power to the controller and then the motor. A PCB was made to fit in the plastic box bottom with the triac and its heatsink attached by screws. The speed control potentiometer is fastened through the PCB and box. Its mounting shaft and nut used to fasten the PCB to the bottom of the box. The PCB is a single sided board with the components soldered directly to the copper.

 

[Hopper]

Looks like a good project. Keep us posted on your progress.

 

[BaronJ]

Hi Guys,

As promised some more pictures.
These show the motor and speed controller mounted on the frame. There are some photos of the grinding wheel and the work support table. Note non of this is set in stone yet as I need to make something to control the table.

As you can see from the marks on the grinding wheel I've given it a spin. It put a lovely finish on a lathe tool. I did not run the motor up much above 2000 rpm because there is some vibration that I think is the wheel that is slightly off balance. Having said that, I haven't attempted to true up the wheel either.

Oh the curved bit of tin is a temporary guard to go over the wheel. The wheel is only 1/4" thick and isn't really intended to be used on the side.

 

[DJP]

I had a need to sharpen end mills instead of buying new so I created a simple grinder from scraps in the shop. The motor runs at 3500 rpm and the cutter holder is made from HMW plastic. The screw with wing nut on the end limits cutter position and the diamond bit on the end is for wheel dressing. I created a sleeve to hold 3/8 inch shank cutters which covers most of my needs.

4 flute cutters are easily sharpened and only the centre needs to be relieved by hand on a bench grinder.

I kept my tool grinder simple because it gets so little use but it feels good to be able to have sharp tools when I need them.

Many of the steps in your project were the same for me.

 

[BaronJ]

Hi DJP,
I like the plastic jar lid used as a wheel guard. I've been toying with using an underground drainage pipe joint to make a protective cover for the motor. You get a nice tickle if your knuckle touches a brush holder when you go to adjust the speed control knob.

One of the criteria I had for mine was to be able to accurately grind lathe tools and sharpen drills with four facets. Grinding slot drills and end mills hadn't occurred to me until you mentioned it. I guess that I will need to obtain a dished wheel to do those.

The plastic/perspex parts are an adjustable removable table so that I can set up to grind thread cutting tools. I have a lot of work to do to make the fittings for the drill grinding attachment.

 

[DJP]

A plastic motor cover makes good sense mostly to keep grinding dust out of the bearings. I have a simple plastic cover which is not in the picture but the motor needs air to stay cool so there are some trade offs. The plastic mayo jar lid captures dust more than providing safety protection. Working from the side of the cup wheel seems safe enough to me.

I learned to sharpen drill bits by hand and I do the same for lathe bits. A green wheel for carbide works well enough and I have made carbide insert holders which limit the amount of sharpening required. It was the milling cutters that were hard to sharpen by hand. One sharpened flute was usually was doing the work so I needed a cup wheel and jig to sharpen four flutes.

Your pictures of construction steps were so similar that I had to post. My (surplus) motor didn't have a capacitor so some electrical work was required. I turned an aluminium hub for the small metric shaft that would also hold the small cup wheel. I fussed with whether 3500 rpm was fast enough. It was.

This is one of those projects where the prototype is good enough to get the job done so I doubt that I'll build a better tool grinder like yours.

 

[BaronJ]

Hi DJP,

A plastic motor cover makes good sense mostly to keep grinding dust out of the bearings. I have a simple plastic cover which is not in the picture but the motor needs air to stay cool so there are some trade offs. The plastic mayo jar lid captures dust more than providing safety protection. Working from the side of the cup wheel seems safe enough to me.

I agree with you about the motor cooling ! It would be nice to have a fan on the motor shaft blowing air over it. I'll have to keep an eye on the temperature when I start to use it in anger. I don't see any problem with using a cup wheel like you are doing. My concern is that side pressure on my wheel which is only 1/4" inch thick, could cause the wheel to burst. The other concern is failure of the Triac that is used to control the speed. These like to fail short circuit ! If that happens the motor will take off at maximum rpm, about 26,000 rpm which is way over the safe 5200 rpm speed for my wheel.

I learned to sharpen drill bits by hand and I do the same for lathe bits. A green wheel for carbide works well enough and I have made carbide insert holders which limit the amount of sharpening required. It was the milling cutters that were hard to sharpen by hand. One sharpened flute was usually was doing the work so I needed a cup wheel and jig to sharpen four flutes.

Whilst I can sharpen drills by hand, after a fashion, I really need to make a jig to help get them just right. My eyesight isn't what it was either...

Your pictures of construction steps were so similar that I had to post. My (surplus) motor didn't have a capacitor so some electrical work was required. I turned an aluminium hub for the small metric shaft that would also hold the small cup wheel. I fussed with whether 3500 rpm was fast enough. It was.

This is one of those projects where the prototype is good enough to get the job done so I doubt that I'll build a better tool grinder like yours.

I wouldn't say that mine is particularly brilliant ! Really just a means to an end. Having a motor handy and some bits of 1/4" plate helped though.

Any more pictures of your tool holder ?

 

[DJP]

Instead of a TriAC consider a fixed step down transformer or just a resistor in series. A household light bulb may work. Once you get a good speed for the tool there isn't much need to make it variable, in my opinion.

I'll take additional pictures for you of the tool holder. Consider it a T square that runs along the aluminium fence in front of the cup wheel. I cut one flute at a time then rotate the cutter in the holder and lock it down for the second cut, then third, then fourth cuts. It's a good set up as even if the T square doesn't follow the fence exactly on the first pass you can repeat until the wheel no longer cuts.

I saw a simpler holder which is just a square block with a hole in the middle to hold the milling cutter. The block is flipped in each side to cut each flute. You then only need an angled surface to run along. My sharpening angle is fixed at 12 degrees which isn't optimal but it works.

Even though this was built from scraps and with many compromises, having sharp milling cutters is priceless.

 

[DJP]

Here is a better picture of the milling cutter holder. One end holds the milling cutter at a fixed depth and orientation to the wheel while the other end holds a diamond tipped tool used to dress the wheel. I used HMW plastic for this holder as it slides easily on a flat surface and against the fence. HMW plastic is strong enough for threaded bolts making it good for jigs.

I bored out the holder for 1/2 inch cutters and made an insert for 3/8 cutters. I may still make bushings for smaller sizes.

Hope this gives you some ideas for your project.

 

[BaronJ]

Here is a better picture of the milling cutter holder. One end holds the milling cutter at a fixed depth and orientation to the wheel while the other end holds a diamond tipped tool used to dress the wheel. I used HMW plastic for this holder as it slides easily on a flat surface and against the fence. HMW plastic is strong enough for threaded bolts making it good for jigs.

I bored out the holder for 1/2 inch cutters and made an insert for 3/8 cutters. I may still make bushings for smaller sizes.

Hope this gives you some ideas for your project.

Thanks for the picture. Yes it helps. I've some plastic that would do that job just fine. I'll have to have a play with some ideas. That is when I can get some new gears for the mill...

I was slitting some aluminium plate earlier and suddenly the mill jammed for a fraction of a second and then suddenly ran free. It has destroyed the driving gear from the motor. After removing the gear I discovered that the spindle had a rough spot, so I stripped the gearbox down to find that the gear in there was not what it should be ! Right from new the machine sounded odd, but I let it carry on thinking that it was just a running in noise. It appears that the twin gear was not machined properly or that the gear had swarf between the teeth.

Either way I'm now out of action with the mill until I can get new gears. At the moment I'm inclined to throw the whole thing in the scrap bin. Plastic gears have no use being in what should be good machines. :rant::rant:

 

[DJP]

My first mill was a mini type with plastic gears. The circuit board is critical as it senses a spike in current to shut the machine down and save the gears from damage. Your circuit board may be defective. I was tempted to remove the circuit board and run the motor on DC but decided against it. Some have converted their mini mill to run off a belt and scrap the gear box entirely. That would be my preference but when I bought the machine I also bought a spare set of gears. With light use gear damage has not been a issue for me.

My second mill is an old Burke which is a heavy duty work horse. A Bridgeport is still the final solution. Someday.

If you had a working mill you could cut a new gear easily. I cut one for my wife's 45 year old Braun kitchen machine. The old gear is used to control the indexing of a shaft on which a gear blank is mounted. A specially ground fly cutter was good enough to form the shape of each gear tooth. The resulting gear was noisy but it worked and I cut two more as spares. The kitchen machine is good for at least another 150 years.

 

[goldstar31]

If you have plastic, why not turn it to size and use your stripped gear as a template and use your lathe as a planer? Otherwise, put in pegs of plastic into the stripped teeth- and use a soldering iron hot to make new teeth.

The idea is from using PTFE candles to repair gouged ski bottoms.

Regards

N

 

[BaronJ]

If you have plastic, why not turn it to size and use your stripped gear as a template and use your lathe as a planer? Otherwise, put in pegs of plastic into the stripped teeth- and use a soldering iron hot to make new teeth.

The idea is from using PTFE candles to repair gouged ski bottoms.

Regards

N

Hi Guys,
Having calmed down now. I agree that making new gears would be one way to go. My inclination would be to use brass for both. Having spoken to the supplier, they are going to send me a pair of new gears. I did make a point of letting them know about the sand, grit and other debris in the gearbox, not that I think it will make any difference. :fan:

The third picture going down are pictures of the dual/duplex gear that sits in the two speed box and directly drives the spindle. Difficult to see in the pictures but the small gear is actually machined off centre by about 50 thou (1.3 mm) whilst the large gear has not been used at all and the teeth are in good condition.

I don't have a problem making a gear cutter for use on the lathe. The hard part would be indexing to produce 61 and 41 teeth accurately for the dual gear and 36 helical teeth on the smaller one. Now if I had a mill... :hDe:

Ah well ! Maybe next week.

 

[BaronJ]

Hi Guys,

Having looked around I have decided that it would be more cost effective in both money and time to replace the plastic dual gear with steel.

I found that I could buy suitable gears off the shelf quite economically direct from a UK manufacturer.

The pictures are two of the gears that I bought to do the job.

 

[DJP]

There must be some reason that plastic was chosen for gears. By upgrading these two you may have just moved the problem to the next plastic gear in the set. I think that there are five gears in the package of spares that I purchased.

What about noise and lubrication? My old Southbend lathe has the gears exposed for easy oiling and they require some adjustment to ensure engagement doesn't generate noise. I am interested in how these issues are resolved for your project.

I still like the ideal of a belt from the motor to the spindle for quiet smooth operation and with a DC motor variable speed control is easy.

I have to admit that one reason for purchase of a spare set of plastic gears was to cut a steel or nylon set myself without losing use of the mill.

 

[BaronJ]

Hi DJP,

There must be some reason that plastic was chosen for gears. By upgrading these two you may have just moved the problem to the next plastic gear in the set. I think that there are five gears in the package of spares that I purchased.

There are only two plastic gears in mine. One small 38 tooth helical 7.5dg 1.25 mod and the duplex/dual gear which is 42 and 62 teeth 1 mod straight tooth which drives the steel spindle gear which is also a duplex/dual gear.

What about noise and lubrication? My old Southbend lathe has the gears exposed for easy oiling and they require some adjustment to ensure engagement doesn't generate noise. I am interested in how these issues are resolved for your project.

I doubt that gear noise is going to be an issue ! Although that is the excuse that is given for the use of plastic gears. My Myford lathe uses steel gears and makes very little noise at all. Actually back gear is the most noisy.

I still like the ideal of a belt from the motor to the spindle for quiet smooth operation and with a DC motor variable speed control is easy.

It wouldn't be too difficult to modify this mill for belt drive. However it would be very difficult to remove the duplex gear without major surgery. Its much more straight forward to do exactly what I am going to do by replacing the plastic duplex gear with a steel equivalent. This also allows me the option of using the small helical plastic gear as a form of shear pin.

I have to admit that one reason for purchase of a spare set of plastic gears was to cut a steel or nylon set myself without losing use of the mill.

I don't know where you are but I was pleasantly surprised by how economical buying steel gears was, even to the point that they were available off the shelf. OK I have to do some machining, but hey we are supposed to be "Experimental Engineers" are we not !

 

[BaronJ]

Well I got some work done on machining the bits for the new gears.

I made a plug gauge so that I got the brass sleeve bore right. I also made a set of soft jaws to hold the gear so that I didn't damage the teeth whilst boring the centre out. I've included a picture of the original gear assembly so you can see how it all fits together.

 

[Swifty]

I like your soft jaw setup, if I want to use soft jaws I will have to buy a new chuck, but I will keep your design in mind.

Paul.

 

[goldstar31]

Soft jaws. All that I do for a one off is to cut 3 bits of copper tube to put over the hard jaws and skim.
I,m a lazy beggar and where I started off serious tool grinding was buy a cheap 6" Chinese or summation grinder, hoist the concrete abrasive wheels and replace them with decent white Aloxite ones. my first rests were wood but mark Two wa one of those cheap Taiwanese two way vices.which got the vice milled off and was replaced with a better tool holder. OK, I,ve got some vastly better stuff now but that was the start.
Let,s look at this tool grinding rationally. The first thing is grit. It gets everywhere. I made up one of those Worden things which got dumped because of grit binding the slides. My Quorn wa. One helluva thing to make but again it has felt grit excluders ans covers and is still a bloody nightmare!
My Clarkson and my little Stent suffere least. Arguably, the Kennet is the simplest and the easiest to set up. I was talking to Arnold Throp who had designed the adore part of DoreWestbury milling machine, had made a and described how he had made a Quorn in his Milling book. He used the little Kennet most times. I suppose like me.

I hope that the foregoing expands but does not detract was has been written earlier.

Norman

 

[goldstar31]

Apologies but this was written in some stately Scottish ruin on an unfamiliar iPad.

,an ah that
Norman