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Progress with my lathe.

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tobias

Wed Dec 02 2015, 11:55AM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Ash,

I would not mount a grounding wheel in the lathe. The abrasive dust will get into the rails and other moving parts in the lathe and over time (a long time) it will increase the clearances. If the spindle has a thru hole for material feed I would make a shaft to mount it on the opposite side.

hen918

Wed Dec 02 2015, 06:56PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

I completely agree with Tobias, grinding dust often ruins slides of a machines designed to do grinding, let alone the slides of a lathe.

I have only seen one lathe - grinder conversion: someone just bolted a big three-phase motor to a table of a old Colchester and turned it into a lethal death machine. Quite apart from the H&S, the lathe was scrap after a few years. (although it was probably scrap before it was converted)

klugesmith

Wed Dec 02 2015, 08:15PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Of course there are lathe jobs that need a grinding wheel, not in the spindle but as a tool for generating precise surfaces on hard materials. You can grind bearing surfaces to finishes and tolerances so close that the work must cool down before it's measured. Newbies can look up "tool post grinder".

In my experience, exposed surfaces on the lathe are all draped with cloth before any toolpost grinder work.
Like covering a surgical patient before the first incision.

Ash Small

Wed Dec 02 2015, 09:43PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yes, it is sensible to take a few precautions. I have bolted an angle grinder to the tool post before. I was just pointing out that it is possible to grind tools using the lathe and a wheel if nothing else is available.

tobias

Thu Dec 03 2015, 11:35AM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

I believe I might be too conservative when doing machine work. There are machines specifically designed for surface grinding, and the surface grinding machines allow tolerances unmatched by a lathe tool post grinder. It's mainly due to the deflection of the part and lower tolerances on bearings and slides in the machine. Some surface grinding machines actually have a "support wheel" on the opposite side of the grinding wheel that both provides supports and advances the part during the grinding process.

I understand doing grinding work in a lathe is a good compromise for the hobbyist who does not have access to a machine designed specifically for the job. But if done without the proper care it is bad for the machine and it might be dangerous to the operator. Today it gives me goosebumps to remember using fine grit sandpaper in a lathe to improve surface finish. :)

PS: one can find attachments that "convert" a drill press into a lathe. I would advise against them, too. :)

Ash Small

Thu Dec 03 2015, 05:32PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

tobias wrote ...

I believe I might be too conservative when doing machine work. There are machines specifically designed for surface grinding, and the surface grinding machines allow tolerances unmatched by a lathe tool post grinder. It's mainly due to the deflection of the part and lower tolerances on bearings and slides in the machine. Some surface grinding machines actually have a "support wheel" on the opposite side of the grinding wheel that both provides supports and advances the part during the grinding process.

I understand doing grinding work in a lathe is a good compromise for the hobbyist who does not have access to a machine designed specifically for the job. But if done without the proper care it is bad for the machine and it might be dangerous to the operator. Today it gives me goosebumps to remember using fine grit sandpaper in a lathe to improve surface finish. :)

PS: one can find attachments that "convert" a drill press into a lathe. I would advise against them, too. :)

I disagree. I learned to grind using a surface grinder as a teenager, I think, when I was taught all about 'spark out',

If you apply the same process to any other grinding process, the same levels of accuracy can be accomplished, pretty much.

If you require greater accuracy, just reduce the amount ground in each pass. Bearing backlash, and all those other factors remain constant.

It all comes down to the skill of the operator

(On the surface grinder I used, the workpiece remained bolted to the bed, while the grinding head moved)

tobias

Thu Dec 03 2015, 05:55PM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Well, we agree to disagree :)

Going back to the controls, not sure if you already finished it but all this discussion reminded me of a lathe I used to operate that had a 5-position lever. ON (top), Coast, Break (center), Coast, REV (lower position). The lever was bolted to the car. I believe the center position shortened all windings in the motor causing it to stop way faster than to just keep them openned. I loved that. The circuit should be interesting.

Ash Small

Thu Dec 03 2015, 07:49PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

tobias wrote ...

Well, we agree to disagree :)

Going back to the controls, not sure if you already finished it but all this discussion reminded me of a lathe I used to operate that had a 5-position lever. ON (top), Coast, Break (center), Coast, REV (lower position). The lever was bolted to the car. I believe the center position shortened all windings in the motor causing it to stop way faster than to just keep them openned. I loved that. The circuit should be interesting.

I was just pointing out that a common mistake a lot of people seem to make is trying to take too much off in one pass, and not waiting for full 'spark out'.

I've used lathes like that in the past too, I often wondered how they stopped so quick. I think the belts would slip if I implemented that on mine, I usually run mine with the reduction gear, so it's not usually a problem anyway.

Ash Small

Fri Nov 18 2016, 02:53AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Well, I finally got it running earlier this week, and have now made a new chuck key as I've not found the old one yet, already to continue with several projects that have been on hold until it was working again.

I only currently have one direction of rotation, but it's now wired through an MEM switch and and NVT switch, as opposed to just a plug on a frayed lead.

I did design another control circuiy last year utilising three relays, but my laptop died before I could post them and I've still not managed to retrieve the data from the hard drive. I do remember that the new circuit did away with the NVT switch, and had two push buttons, one for start and one for stop on the 24V circuit.

I don't yet have a coolant pump wired in, I need to rig up a tray to catch it first, but I can use it for a number of jobs I have that don't require coolant.

I should be able to start posting details of progress with some of my other projects now

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