Home-Made Slow-Speed Grinder

[Dr.Al]

This is my home-made slow-speed grinder. It's based on an idea from Stefan Gotteswinter, although everything in my version was designed from scratch. It uses 150 mm diameter diamond grinding discs, which are cheap (the ones I bought were about £5 each) and have the advantage (compared to conventional grinding wheels) of being flat so surfaces prepared on the grinding disc can then be easily honed on a whetstone or waterstone.



Mostly made from aluminium flat bar (15 × 100 mm and 8 × 200 mm), with a 0.8 mm mild steel cover, shafts made from EN1A steel and gears made from steel and acetal.



It can also be placed on its back (and in fact this is how I most often use it) for grinding steeper angles; the table can be placed in two positions - the one shown in these photos for normal operation or in a higher position for grinding wider tools.



The table and fence keep the tool to be sharpened square to the disc, so it's really useful for reshaping second-hand tools that have been sharpened a long way off square. The low running speed (up to 400 rpm) keeps the tool from getting too hot.



The reference surface is parallel and coplanar with the disc so can be used with a honing guide as an alternative to using the table. This is particularly useful as the edge can be shaped on the grinder and then the honing guide can be transferred to a fine grit waterstone for final sharpening.

There are lots more photos (including internal ones and higher-resolution copies of the ones above) and details on my website: https://www.cgtk.co.uk/metalwork/gri...owspeedgrinder

[DIYer]

Thanks Dr.Al! We've added your Slow Speed Grinder to our Grinding category,
as well as to your builder page: Dr.Al's Homemade Tools. Your receipt:

Slow Speed Grinder by Dr.Al

tags: grinder, disc

[DIYSwede]

-Thanks Dr Al, and welcome back! Amazed nobody haven't commented on this build yet.
Really clever and nice build, and thanks for the link to the excellent description on your site.
Your flat and parallel, adjustable honing surface is a first for me - haven't seen that one ever...

Q: Given the neodymium magnet disk hold, do you get any residual magnetism in & grinding dust sticking to the disks after use?
How far below the disk surface did you set the magnets? Did you cut your gears by conventional mill/ dividing head methods?

I've scored a cheap n cheery (BG) set of disks myself, intending something of the like:
merely 3 "drive dog" 3 mm dowel pins (120 degs apart)
protruding 1,5 mm and giving the 1/2" centre a 2,5 mm stick-out
for easy placing/ turning the disk into its magnetic hold position.
Incidentally I've already dumpster-dived a 150W 24V sealed DC motor from an electric kickboard,
a 20A cheapo PWM controller
and a 30VDC 7A PSU of the same ilk as yours for my Zero-cash backburner grinder project.

Just a few thoughts and questions - thanks again for sharing such an inspiring build!

ATB

Johan

[tblaze92143]

What is the power source?

[DIYSwede]

What is the power source?

A 230 V AC outlet...

-Seriously, you could find all the ingenious construction details including its drive system thru this link:
https://www.cgtk.co.uk/metalwork/gri...owspeedgrinder

[DIYSwede]

Just wanted to share yet another useful page* of Dr Al's:

Metric Gear Calculator/ DXF and/ or SVG Generator



Dr.Al's Metric prescription: "I wrote this calculator after getting frustrated with the number of calculators on the web
that focus on antiquated diametral pitch based gears rather than modern module gears."

Available at: https://www.cgtk.co.uk/metalwork/calculators/gears

* Many other pages of his might also be worth visiting... https://www.cgtk.co.uk/metalwork/

"I'm NOT affiliated, yada, yada..."

Johan

[tblaze92143]

OOPS! I should have asked: "what motor is the grinder powered with?" . I looked at the info on the link and found the answer. I"m thinking of using a variable speed motor off a treadmill that I bought for $25. I will post results "when I get around to making it".

[Jon]

Congratulations Dr.Al - your Slow Speed Grinder is the Homemade Tool of the Week!

This is a well-executed and useful tool build, with excellent documentation both here and on your website.

Some more good builds from this week:

Filing Rest by uv8452
Electrolytic Brush by Claudio HG
Electronic Lathe Controller by tonyfoale
Knife Vise by fox craft
Quick Change Tool Holder Storage by mylilmule
Folding Leg Workbench by tado creation
Collection of Homemade Tools by ttmrj
Workbench Drill Mount by orioncons36
Miniature Optical Center Punch by editor@glue-it.com
Aluminum Sheetstock Deburring Method by rgsparber
Grinding Drum by editor@glue-it.com
Drill Press Vise by Vyacheslav.Nevolya
Boring Bar by Salix84
Pegboard by Tuomas
Collection of Homemade Tools by theeddies
Woodworking Clamps by orioncons36

Dr.Al - we've added your tool entry to our All Homemade Tool of the Week winners post. And, you'll now notice the wrench-on-pedestal award in the awards showcase in your postbit, visible beneath your username:



You've also been granted free lifetime Supporting Member status, which means you can now access all of the tool plans and tool ebooks in our Supporters Forum (thanks to mklotz for that idea). And you'll now notice the Supporters award in the awards showcase in your postbit:



You'll be receiving a $25 online gift card, in your choice of Amazon (US-only), PayPal, or bitcoin. Please PM me your current email address and award choice and I'll get it sent over right away.

Nice work!

[uv8452]

Thank you, Jon, for the laudatio.

[Dr.Al]

-Thanks Dr Al, and welcome back! Amazed nobody haven't commented on this build yet.
Really clever and nice build, and thanks for the link to the excellent description on your site.
Your flat and parallel, adjustable honing surface is a first for me - haven't seen that one ever...

Q: Given the neodymium magnet disk hold, do you get any residual magnetism in & grinding dust sticking to the disks after use?
How far below the disk surface did you set the magnets? Did you cut your gears by conventional mill/ dividing head methods?

Sorry for the slow reply - I somehow missed that anyone had replied to this thread until today. In answer to your questions, yes - there's a bit of grinding metal dust sticking to the discs, but I generally find it just wipes off fairly easily, so any residual magnetism is pretty weak. The magnets are flush with the surface and yes, the gears were cut with a dividing head and some Chinese gear cutters. I've cut gears using Mike Cox's method before but decided in the end that it was worth buying some cheap module 1 cutters.

I've scored a cheap n cheery (BG) set of disks myself, intending something of the like:
merely 3 "drive dog" 3 mm dowel pins (120 degs apart)
protruding 1,5 mm and giving the 1/2" centre a 2,5 mm stick-out
for easy placing/ turning the disk into its magnetic hold position.
Incidentally I've already dumpster-dived a 150W 24V sealed DC motor from an electric kickboard,
a 20A cheapo PWM controller
and a 30VDC 7A PSU of the same ilk as yours for my Zero-cash backburner grinder project.

Just a few thoughts and questions - thanks again for sharing such an inspiring build!

ATB

Johan

I'll look forward to seeing what you come up with - that sounds like a good project.

What is the power source?

OOPS! I should have asked: "what motor is the grinder powered with?" . I looked at the info on the link and found the answer. I"m thinking of using a variable speed motor off a treadmill that I bought for $25. I will post results "when I get around to making it".

It looks like you've figured out the answer to that, but for anyone else who comes looking it's a 250 W 24 V permanent magnet brushed DC motor. I think it was originally designed for a lorry windscreen washer system or something like that, but it had been repurposed by the company at which I worked for one of their products. At the end of the product development cycle, a load of motors that had been used for testing got chucked out. I got three of them and this is one.