KMG Grinder build in progress

[RickA]

Hi everyone

As mentioned in my 1st knife posting I am currently busy building a KMG grinder.

I have read quite a lot about various grinder designs in the past couple of months, and while I really like the EERF grinder design (http://blindhogg.com/eerfgrinder.html), with the motor mounted directly on the frame, ideally this seems to require a 3Phase motor and VFD which I don't have.

I will be using a 220V single phase, 1.1KW(1.5HP) pool pump motor, which runs at 2850rpm, so I will need to use step pulleys for variable speeds and the KMG design looks better suited to accomodate the step pulleys.

I wasn't able to find some of the steel sizes listed in the KMG design tutorial I got off BritishBlades (http://www.britishblades.com/forums/showthread.php?60352-Let’s-make-a-Grinder) so have adapted the sizes slightly, for instance I could not find the 35x35mm square bar in bright mild steel, so opted for 38.2x38.2mm square Aluminium bar.

I changed parts of the design to accomodate building the grinder using drilling and tapping rather than welding. I have used Michael Clerc's design for some of these mods (http://www.scribd.com/doc/24148558/Grinder-Plans)

I have also had to make some tools to accomodate the drilling/tapping operation. I could not find a tool supplier locally in South Africa who knew what a transfer punch was? so I ended up making my own out of old drill bit shanks, ground to a very shallow point, and they have worked brilliantly in aligning holes to be drilled.

So far I have built the toolarm box, with it's support legs and feet, and have added the tracking arm support post.(still to be cut / fitted for the tracking arm). The next part will be to add the rear bearing mounts for the drive wheel drive shaft / step pulleys, although I will have to make a plan to have these drilled as my current drill press has a max drilling diameter of 10mm in steel, and the drive shaft bearings require a 20mm drive shaft.

I also need to reduce the height of the toolarm box sides by +/- 0.8mm as the vertical play in the toolarm due to the difference in steel size (40mm) vs Alu (38.2mm) appears to be too much (1.8mm). What sort of gap is acceptable here? There will be a tool arm clamp threaded in from the side of the toolarm box? but will this clamp be enough to make up for the large gap?

I also still have to come up with drive wheels, contact wheels etc - I have looked at the possibility of using castor wheels, with decent bearings fitted, however have heard some stories about knife blanks being badly ground due to imbalanced contact wheels so I may just bite the bullet and buy some decent contact wheels (very expensive here in South Africa).

See below for a couple of photos of the grinder build so far!
Thanks
Rick

 

[Wayne Coe]

That motor is awfully fast for a step pulley type grinder. I can supply the VFD and 3 phase motor. I recently sent a VFD to Australia and the shipping cost was about $55.00. A 3 phase motor would be more than that because of weight but we could check it out. You could probably find a 3 phase motor there. I suggest about 1800 rpm motors and the VFD set to run the motor at double speed. The motors that I sell are designed to do that. Look at my forum at: http://knifedogs.com/forumdisplay.php?133-Wayne-Coe-Artist-Blacksmith You may find some good information there. Let me know if I can answer any questions or help you.

 

[RickA]

Hi Wayne

Thanks for the advice, I know that the motor's original speed is too fast for grinding, however there are quite a few chaps locally who have gone this route, using step pulleys.

I would like a 3Phase / VFD setup, but at this stage I just don't have the budget. The 3phase motor and VFD in SA would cost me around R4000.00, which is more than triple the cost of the grinder so far.
I will probably convert to a 3Ph/VFD setup as soon as I could afford it, but for now will have to make do. Any idea what sort of speeds would i be looking at with the 5 step pulleys which I have on order? They are pulleys as used in a mid sized drill press (700W) - don't have details of diameters etc?

Thanks for the suggestion on 1800RPM motors. I will spend some time reading your forum to get some ideas.
Best Regards
Rick

 

[Wayne Coe]

I don't know the formulas for figuring out the speed that you will be running. I think that somewhere in the last year or so someone posted on KD how to figure that. I do know that running at 3600 rpm is faaaaaaast.

 

[Sean Cochran]

Looking good so far.

 

[seionage]

watching this with interest! Thanks for posting.

 

[Pieter]

Rick looking good. I also used the same set of plans and I am building 2 grinders using 1 motor. Will do a WIP soon.

 

[RickA]

Hi Pieter

Thanks for the feedback, I would be interested to see your WIP. I saw a KMG on Youtube where the builder had also incorporated a disc grinder at the back on the right - basically the disc, was attached to an extension off the drive wheel. Looks nice too, I thought it might be something to add in future, unless i build a disc grinder as an alternative.

What motor are you using for your build? I would like a 3phase with VFD speed control, but 3phase motors (from what I have seen) are expensive, not to mention the VFD's are not cheap either

Regards
Rick

 

[Wayne Coe]

Actually Rick, 3 phase motors should be a little cheaper. Maybe it has to do with supply and demand.

 

[RickA]

Hi Wayne

After your first reply, I started to do some searching and I found a local supplier in South Africa who specialise in motors and VFD's, and combination packages for knifemakers. The price for a 1.5KW 3phase 220V motor (1440RPM) + VFD is around R3300 excl VAT, so around $500 for a motor + VFD, which isn't too bad, although still out of my budget at the moment. If I can sell one of my older mountain bikes I could buy one, so maybe I will wait a while and rather get the 3Phase + VFD

Thanks
Rick

 

[Pieter]

Hi Rick

Wayne is correct. 3 phase motors are cheaper than single phase motors and that is, IMHO the only way to go. I have just recently started to hollow grinding on a friends machine and the controle is unreal if the wheel is running slow. The better you get the faster the wheel can be turning. Polishing is also done better at lower speeds.

I am also mounting 2 sanding discs on my drive shaft 1 on either side. Here is a picture of where I am at the moment.

 

[RickA]

Hi Pieter

I did some searching today and found a motor / VFD supplier in Pretoria (cfptech.co.za), their prices look pretty good although at the moment I don't have the budget. I was hoping to use the 1.1Kw pool pump motor I have with step pulleys. I need to find the maths to calculate the belt speed / rpm i would get with the step pulleys, taking a look at the speed table on my drill press - starting with a 1400RPM motor, the pulleys allow for speeds from 515 rpm up to 2850 rpm, so given the 2840 rpm of the pool pump motor, logic would tell me that my minimum speed will be around 1030 rpm? with a maximum of around 5500 (Ridiculous speeds).

I'm going to have to get a 3phase motor, which are actually fairly cheap as you said +/- R1400 ex VAT for a 1.5KW 3Phase 220V motor from CFP, so I could always start with the motor and step pulleys and then convert to VFD in future.

Where are you getting the sanding Discs from? KMTS?

Regards
Rick



Where did you get the drive shaft? Did you make it? I still need to sort that out too. The bearings I got have a 20mm inside diameter.

 

[RickA]

Hi Everyone

I took a couple more photos of the KMG today, I am busy with the tracking arm at the moment, so far I have completed the tracking arm mount, and the tracking arm pivot (I had to adapt the tracking pivot to suit the steel I had, and the construction method (Drill & tap - as opposed to welding). Next step is to add the Tracking arm tension spring, and the tracking arm handle (need to find one, most engineering supply stores around here are closed for the Christmas - New Year period, so I have not had much luck finding handles / springs this week.

Wayne - I realised that my last comment re getting a 3phase motor and using it with step pulleys initially would not be possible without the VFD since I only have single phase power in my shop!! Looks like I am stuck - either using the high speed single phase motor or spending the money for the 3Phase + VFD. ( I know this is the way to go, but my bank manager doesn't agree at the moment!)

Regards
Rick

 

[Pieter]

Rick be careful you can not run a 3 phase 220 V motor with out the VFD. The VFD uses single phase 220 V input and give you 3 phase 220 V output, so if you are going that route you need to get both or go 220 V single phase with step pulleys. You need to shop around on that 3 phase motor you should get one for less than R 1000.00 exc VAT.

Yes I get some of my equipment at KMT's but look at Herbst knifes website there equipment is a lot cheaper.

Yes I made my own shaft and it is 20mm as well.

PM me that I can send my cell no. and you can phone me for more info.

 

[RickA]

Hi Pieter

Thanks for the advice, I did realise that after I had written it (weird I didn't immediately think of it, considering I am an Electrical Engineer by trade). I will definitely be going for the Three Phase + VFD (when my budget allows).

I have done a fair amount of searching in Cape Town and haven't managed to find a 3Phase motor under R1000, in fact the motors at CFPTech as mentioned in my previous post look cheap compared to some of the pricing I have seen here.

Where did you source the Tracking arm springs? Are you getting the drive wheels / contact wheels from Herbst too?

Thanks
Rick
I will PM you shortly, thanks.

I

As for the VFD's, It doesn't seem possible to find one for less than R2000+.

 

[Pieter]

Rick that is about what the VFD would cost you and yes I did get my contact wheels from Herbst, I actualy did a knife making coarse with them aswell. As for the springs I found them at an industrial supplier.

 

[RickA]

Hi Pieter

Thanks - I will have to look around for a spring supplier here, as for the drive shaft - did you make it from standard 20mm bright mild steel rod?

I was up in JHB in August for work, and tried to book with Herbst to do one of their courses the same week I was there, as it would have been easy to extend my stay by a couple of days, but they were fully booked for that weekend. I would still like to do a course or two (Fixed blade followed by folder) however it is difficult from Cape Town, unless I can time it to coincide with a work trip. Luckily I have found a couple of guys in Cape Town who give courses, and I will probably do a course in Feb.

Thanks again
Rick

 

[RickA]

Hi Everyone

I made some progress with the grinder today, finishing off the Bearing carriers at the back of the frame (except for drilling and mounting the bearings - which will take some workarounds!) I need to drill a 20mm+ hole (probably 25mm / 1") for the driveshaft, and two 10mm holes for the bearing mount holes - the challenge is that I only have a small drill press which is specced to drill 8.5mm max dia in mild steel, as for using a bi-metal hole saw - my drill press will not go slower than 550rpm, which is about 150-200rpm faster than the recommended speed on the hole saw?? Not sure how this will work - I may end up having to chain drill a circle, cut out the center and file to shape.

Most of the local industrial supply stores locally still seem to be closed this week and I have not yet been able to source a spring or handle for the tracking arm. So this morning I decided to make a handle out of 16mm bright mild steel rod, which worked out perfectly, and then this afternoon I came across what could turn out to be the perfect tracking arm tension spring in my local hardware store - (a gate closer, which is a 22cm long spring with two aluminum spring platforms - shown in the photos below. I will have to shorten the spring, which is fine, but it should work perfectly, and the spring platforms give me the perfect base / top for the tension spring, although I might have to shorten one of them a bit).

So far it has come along nicely, it has been a bit slow, having to drill and tap so many holes, after first ensuring that they are aligned (thank goodness for transfer punches - or rather, since I could not get any in South Africa, the homemade transfer punches I made to assist in lining up everything).

Let me know what you think of it so far

Thanks
Rick

 

[Pieter]

Rick comming along nicely.

 

[tedinatl]

That is coming along very nicely. I'm thinking of starting to build one of these over a period of time as I get funds/time/motivation. Thanks for going through the effort of posting this - I'll definitely refer back to it once I start!