NOTE: This is waiting for me to take some additional/corrected photos, but it is fine for the confident DIYer.
Here I'm going to show you how I converted a cheap bench grinder into one that can be used with lathe tool sharpening accessories intended for much more expensive grinders. This is by no means a perfect solution or a replacement for the proper tools, but it will bridge the gap.
If you don't fancy this, but want to sharpen on the cheap there are many guides for making a wooden jig that will work as well. But if happen to have some accessories, but no bar to rest them on, read on.
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Step 1: Overview
The basic idea is simple. Most cheap bench grinders have guards that cover almost the entire disc, they are like cases with a small gap. This makes sharpening lathe tools quite difficult because so little of the disc is exposed. These guards often have a small flange onto which a small tool rest can be attached, usually provided with the grinder. The flange usually projects outwards and can be used to hold a bar a suitable distance from the the disc. However, the flange also blocks the movement of any kind of gouge holding accessory.
The solution is to swap the sides of the guard, remove the center piece so the disc is fully exposed and increase the gap between the two sides of the guard so there is plenty of room to get accessories on the bar with room for movement.
This will involve a bit of metal work but the odds are that if you have a lathe and now a bench grinder then this should be fairly easy for you.
Note that once you have made this conversion it will be possible to more or less go back to the original configuration, but the guards will be permanently damaged (though still largely functional save for the new holes).
SAFETY FIRST: Cutting metal produces metal particles and larger fragments called swarf. These are dangerous to your lungs, eyes, skin and anything electrical. Swarf in particular can make painful splinters and cause serious damage to your eyes. Always wear appropriate safety equipment (gloves, safety glasses, dust mask) and clean up immediately after each metal working session, paying particular attention to prevent debris falling inside anything electrical or clothing. There is also a potential fire hazard cutting metal, you should have fire safety equipment in your work area anyway. Naturally you will have a first aid kit available and are either using an RCD consumer unit in your work area or are using plugin RCDs. Electric shocks hurt and can kill.
Keep pets and children away!
I cannot accept any responsibility for any damage or injury howsoever caused by you carrying out this modification to your bench grinder.
Step 2: You Will Need
- A bench grinder. I used a cheap own brand one from a national DIY chain. Two of the larger national chains stock identical grinders, they differ only by colour, label and amazingly price. It has a disc either side, guards that almost entirely encase the discs and is about as basic as basic gets. Mine has 6" diameter discs but this should work for 8" as well. Crucially, each guard has a projection to mount a small tool rest.
- 3 x M5x70mm and 3 x M5x20mm machine screws. If they don't come with nuts, buy a packet, you will need 9 so buy spares. Anti-rattle washers to fit, you will need 9, again buy spares as well.
- A means to cut spot welds, such as a mini drill with cutting discs. You may find that your guards are constructed differently and you will need different means to take it apart.
- A metal rod, one that fits snugly through the tool rest slots on the guards. This needs to be strong enough so as not to flex when only supported by the ends and long enough to easily go from one side of the grinder to the other. I used one that is a depth gauge for a drill press, but such bars should be readily available from a good DIY store.
- Spanners to remove discs from the grinder, should have been provided with the grinder.
- Screwdriver(s) to fit the machine screws
- Spanner or pliers to hold the machine screw nuts
- Drill with metal cutting bits that match the diameter of the holes holding the guard to the grinder body (5mm or 3/16"). You will also need to cut a suitable hole to get one part of the guard over the axle. This can be drilled, cut or grinded.
Step 3: Method
- Unplug the grinder, do not plug it in again until you have completed all the steps below.
- Remove both discs and guards. This usually involves removing the outer side from the guard, removing a nut and sliding the disc off. You should then see some small screws that attach the guard to the body, remove the screws from both guards and remove the guards.
- For ONE guard only. Examine the removed guard and there are probably 3 spot welds holding the central shield in place, these need to be cut. Whilst it might be possible to snap them by flexing the shield, it may also cause the metal to fracture in the wrong place. A mini drill will make short work of the welds but be careful with the cutting discs, they can explode! The separated shield is no longer needed.
- The second guard can be reattached to the body but rotated so that the tool rest flange is pointing to your face in normal grinder usage. This may mean that only two of the screws can be replaced.
- The two sides of the dismantled guard need to be bolted together so that the body side piece is on top of the outer side, this will serve as a template for the new holes. You may want to offer the sides up to see which way round you want to do this. I did mine with the sides on top of each other rather than facing each other as there was less chance of slippage when drilling.
- When assembled you need to drill out fixing holes to attach to the body and a large central hole to allow the axle through. Remember, the outer side of the guard is now the body side of the guard so it needs the same holes. On my grinder, the outer side of the guard was domed which made drilling holes more difficult, hence I used the other side as a template and to stop the drill bit sliding down the side of the dome.
- With the new holes attach the new body guard to the body, rotating it so that the flange is pointing towards you as you did with the other guard. If you find that only two screws fit you may have a problem with the guard not being parallel to the body and catching on the disc. You have two choices a) drill a new hole to line up with the third hole in the body and tighten all screws evenly or b) use a wedge between the body and the guard, half way between the two screws, to level the guard out. However you attach it, you must ensure the guard is parallel to the body otherwise you risk it being caught on the disc.
- Attach the disc. Manually turn the disc and ensure it is suitably attached and does not catch on the guard.
- Using the long bolts, attach the other side of the guard. Use the nuts to ensure the outer guard cannot slide down the bolts and that the bolts cannot slide either way through the other side of the guard. This will ensure the outer guard is held firmly in place.
- Again turn the disc by hand and ensure it cannot possibly catch any part of the guard or the bolts.
- Thread the bar between the two guards using the hole in the tool rest flange. If you have a slot rather than a hole you may need to chock the bar in place with additional nuts and bolts.
- Using whatever gouge holding accessories you have, place them on the bar and ensure it does not catch on the body side of the guard. If it does you may need to cut it back a bit or possibly even reposition the bolt.
- You're done. But before you go sharpening mad, stand well back and turn the grinder on. Make sure nothing comes off or rattles, it should sound and act no differently to before your modification. If all is well, gently, try some sharpening.
Carry on through this instructable to see detailed instructions with photos.
Step 4: Remove Discs and Guards
Follow the instructions provided with your grinder to remove the discs, for mine and I suspect many other cheap grinders, it will be like this.
Remove any fixtures on the guards such as tool rests and safety screens.
The guard is held together with three machine screws, undo them to remove the outer cover. Inside you will see the disc held on by a large nut and a metal disc. The nuts on either side turn in different directions and cannot be swapped. Remove the discs and any fittings.
With the discs removed there are a further three screws holding each guard to the body, remove them and remove the guards.
Step 5: Dismantle ONE Guard
You need to decide which side you are going to working. I used the right hand side of the grinder. If you want to use the left side instead I suggest you familiarise yourself with all the steps first and then modify them as necessary.
Examine the guard, you will probably find the side is attached to the central shield with spot welds, there were three in my case. Using a means of your choice you need to cut these welds and separate the two parts. If yours is held together by other means you must work out how to separate them, you want only the two sides, unbent and undamaged.
Step 6: Make and Fit the New Guard
The new guard will be composed of the two sides of the guard swapped around. This allows the slot that held the tool rest to be moved far away from the disc allowing plenty of space of accessories to get in whilst also holding the bar.
First of all you need to drill holes into what was the outer side of the guard so that it can be attached to the body like the inner side was. To do this, use one as a template for the other and bolt them together. You will also need to remove the centre of the old outer side so it will fit over the axle. You can drill, cut or grind this.
Your newly drilled side can be fastened to the side of body using the 20mm screws and anti-rattle washers. You need to ensure the opening is on top, this will mean that only two of the screw holes line up. If you do them up fully the guard will be pulled to one side and the disc will catch on it. You have two solutions. Loosen the screws so that the guard can be hung parallel to the side of the body and place a wedge between the guard and the body between the two screws. This will keep the guard in place, you will need to tweak the screws to get it right. However, the large washers that go on the disc will catch on the screws if you are not careful. With each adjustment ensure the disc can spin freely. The other option and ultimately the better solution is to work out where the other screw hole is and drill a new hole. So long as all three screws are done tightly, the guard should be perfectly parallel to the body and no risk of screws catching on anything.
Ensure the disc properly attached and secured and moves freely.
Now using your long machine screws, put them through the old outer side of the guard from what would have been the inside. This is important, if you do it the other way the tool rest slot will be in the wrong place. Puts nuts and anti-rattle washers on tighten the nuts. Now put nuts and anti rattle washers on but only about 1cm from the end of the bolts. Put the bolts through the corresponding holes in the side on the body and put nuts and anti-rattle washers on the ends, do them up tightly.
You should now have a very wide guard attached to the side of the grinder.
Step 7: Fit the Bar
To fit the bar you need to re-attach the other guard suitable rotated so that the tool rest slot lines up with the new guard, again only two screws will fit. Unless you intend to put the disc back on the side then it doesn't matter.
Slide the bar through the two slots. Fit two screws into the slots to stop the bar sliding up and down in the slots. you want the bar as far away from the disc as possible.
Offer up your tool/accessory and check it will fit against the bar and within the guard. I found that I am going to have to trim the guard a bit to ensure I can slide side to side, but it's pretty much there for a fraction of the cost of the real thing.
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