Thread: Power for a toolpost grinder

One of the projects on my "todo" list, this is one link I have bookmarked for that purpose

Toolpost Grinder

Originally Posted by scottyd

Im planning to make a toolpost grinder for my hercus 260 and im tossing up which way to go with powering it. Itll be far from quiet. I also worry about mounting a belt on something thats moving that fast, the belt will need a lot of tension or will surely need to be going around some seriously small pulleys to keep the belt speed down.
Anybody have some wisdom to share?

Proprietory TPGs are definitely not quiet. I have a Waldown C01 and it sounds like a jet taking off. Earmuffs required.

Motor speed on the Waldown from memory is about 12,00 RPM so you will be spinning much faster with the router. An angle grinder is probably closer to the 10 - 12 K Waldown figure.

The Waldown runs a flat fibre belt and tension is very low. The speed shouldn't have any bearing on belt tension.

High reving motors tend to have low torque, and it's better for the belt to slip if the stone gets overloaded. Hence the flat belt drive system.

So maybe think angle grinder as an alternative motor.

Cheers

Rob

I would have said the router might vibrate a bit too much...but clearly by the link Fred (thank you, i'll save that one) posted maybe not. I would find a treadmill personally. I think these DC motors would be great for a TPG, plus you get multi v belts and pulleys plus lots of other usefull stuff...

Another link, this one using a commercially available one, but has some good ideas as well.
It appears to be using the motor and top part of the Sieg X2 Mill.

9x20 Lathe Tool Post Grinder

Also some more details on the RC plane starter motor version in the CNCCookbook link above

Tool Post Grinder. Dovetail Version. - Home Model Engine Machinist

Originally Posted by scottyd

Im planning to make a toolpost grinder for my hercus 260 and im tossing up which way to go with powering it. This obviously has a pretty big bearing on the rest of the assembly, so making this decision is going to determine the layout of the rest of the tool.

You basically have to aim for two spindle speeds.

24,000 rpm for internal
7,00 rpm external (about 80 mm stone)

If you run 40 mm external like I do, you will need to bump up the spindle speed considerably to achieve the correct stone surface speed - which is 32 metres/second.

You can run slower than this if you wish, but the quoted figure is the "safe" stone speed recommended.

Proprietory TPGs like Waldown run two pulley ratios on the motor and separate pulley sizes for the external and internal spindles.

The two pulley ratios on the motor are for the 40 and 80 mm external stone sizes.

Rob

My father built a TPG for his 9in Southbend about 40 years ago, set up with seperate interchangeable spindles for internal and external work. Each spindle had it's own driven pulley. Power was a Singer domestic sewing machine motor driving via its standard pulley and a Singer V belt. My lousy little Sherline lathe uses a similar arrangement, although it offers dual step pulleys at both ends.

Dad's worked quite well and he used it regularly for about 30 years until he went blind and gave up turning.

Hi there Scotty, Fred has provided some excellent links. I have opted for the 'simple' solution to begin with, maybe I'm not as serious as Stuart and others who are busy building a TPG. I have fitted up the angle grinder directly to the tool post. I have to say the results have been better than I expected. So I am now on a WIP to make a mount to fit the Dremel onto the tool post as well.

The disk on the grinder isn't the one I use for facing. To fit the mount, the gear head was removed from the grinder and 3 true faces milled and tapped into the grinder head.

With the angle grinder, I use a 10A rated speed controller from Jaycar - beware, the box says 'Some Assembly required' - that translates to complete assembly required, so if you need one of those, be fairly proficient at building CCT cards or get a mate to build it for you.

I'm surprised by the major efforts constructing TPGs that Fred has exposed and I wonder why so many TPGs are so elaborate? I have had difficulty finding various sized stones - but seemingly someone knows where to get them.

Regards, Daryl

Hi Daryl,
I have used a Dremel in the tool post, but a real tool post grinder will have precision bearings and you can grind to tenth of a thou or less, where our hand grinders and Dremel will have 10 to 100 times that slop in just the bearing etc.
If you grab the grinding disk and pull and push you will see what I mean.

It would be easy to over shoot a bearing fit with this sort of play, so that where a precision grinder comes into it as you can really on it time and time again. For finishing something to a nice look, no problems a hand grinder or Dremel will so, but not for accuracy.

A set of bearings in on of the commercial grinders can cost $300 up as they are selected at the factory for the least run out.

Dave

Originally Posted by Dave J

Hi Daryl,
I have used a Dremel in the tool post, but a real tool post grinder will have precision bearings and you can grind to tenth of an inch or less, where our hand grinders and Dremel will have 10 to 100 times that slop in just the bearing etc.
If you grab the grinding disk and pull and push you will see what I mean.

A set of bearings in on of the commercial grinders can cost $300 up as they are selected at the factory for the least run out.

Dave

The Waldown runs hi speed magneto bearings on the spindles. These cost about $30 each through CBC - so not that expensive.

Dremel type setups can do good work - but only for very light applications.

My video below shows what is possible:

How to sharpen a HSS end mill using a cheap pencil air die grinder - YouTube

Once again, setup is important, you must prevent whip and runout.

I originally was going to go the angle grinder route until the Waldown came along.

I intended to mount the angle grinder differently to what is shown earlier. I don't like the idea of using the single handle mount bolt. I was going to make up a mounting plate which would use the four bolts for the angle head to motor body.

Slightly OT DarBee, hows that lathe going ?

Rob

Thanks for the input folks.

The two motors ive listed are the only two ive got to readily include in this project though. I do see the appeal of the DC treadmill motor, me and my public education income arnt enough to be able to go hunting for one

However, ive dissected the router to have a look-see inside. Dispite being pretty old, its in relatively good shape. I suspect its on its second set of brushes because the ones that are in it have a good deal of length left, though the spindle bearings feel like they dont want to keep playing. Once i figure out how to remove the collet chuck off the bottom of the spindle, itll come apart. Anyone know how theyre mounted on there? I cant find any circlips or see the end of any threads and i dont really want to break an otherwise fine router!

Ive also been doing some research into just how much strain the whole pulley assembly endures. My primary concern with using the router was the belt velocity and the risk of the belt parting company with its pulleys and mating with my face. I needn't have been worried. Some light reading on the gates website suggests that the pulley will usually give up first. Theyre guidelines state that an aluminium pulley will work fine in the 60 to 90m/s surface speed range and all will be well. This means the pulleys need not be microscopic. The driving pulley mounted on the router, for example, can be 72mm across and still be safe. Ill probably aim for a little smaller than that in order to keep the package a convenient size on the ginding wheel arbor. So rather than stressing about belt speed, i shall calculate the size of the master pulley from the other end of the belt, keep the driven pulley smaller than 80mm diameter of the ginding wheel and go from there. Before I can start on that bit I need to find some information on how much power a belt can actually transfer. Id like to keep the belt as small and light as possible to reduce the inefficiencies of thick belts and small pulleys, so does anyone know how much power a 3L or 4L belt can transfer comfortably?

So at this stage, the router is getting the nod as the power.

I have been contemplating building a mounting for my Scintilla Die Grinder to use as a TPG. It has a mounting sleeve on it and has a spindle speed of 30,000 RPM.
Mounted points are available in a huge variety of shapes and sizes from any Pferd agency.

Roger

It may be that the chuck has a LH threaded screw down in the centre of the chuck (collet removed) to lock it in place. As a general rule, the chuck's will be RH threaded and if a securing screw is used down the centre of the spindle, it will likely be a LH thread.

Just a thought. Regards, Daryl

Originally Posted by Dave J

Hi Daryl,
I have used a Dremel in the tool post, but a real tool post grinder will have precision bearings and you can grind to tenth of a thou or less, where our hand grinders and Dremel will have 10 to 100 times that slop in just the bearing etc.
If you grab the grinding disk and pull and push you will see what I mean.

Bingo. Spot on - an angle grinder is a metal butcher's tool. I have 5 or 6 of them. They can be a precise tool, provided your idea of precision is +/- 0.1mm. I'd never even consider using one to obtain a fit to 0.01mm or better that also had to be round and consistent, eg for a bearing. Rather use my lathe and wet & dry paper in kerosene to polish down the last little bit.

I made one from a Singer motor and a commercial work head 30 years or so back. Used it once, was unhappy with the results (which could well have been ignorance and rotten technique) and never bothered since.

Besides I simply don't like the idea of grinding grit anywhere near my lathe.

PDW

Originally Posted by PDW

Bingo. Spot on - an angle grinder is a metal butcher's tool. I have 5 or 6 of them.
Besides I simply don't like the idea of grinding grit anywhere near my lathe.

PDW

If you use the angle grinder to drive a precision spindle, you will get a precision job. It's that simple. I would never using a basic angle grinder as a TPG.

If you use a TPG on a lathe without leadscrew covers, I think you are asking for trouble.

I use my TPG regularly and if you have leadscrew covers and cover, clean and re-oil everything adequately, grit etc is not an issue.

There are no half measures with a TPG - you have to protect the lathe, clean the lathe. Do this and you will not have an issue.

Rob