Making a Sub Spindle

[sbwhart]

Hi Chaps

Quite a few of you chaps have posted pics of sub-spindles is use either cross drilling, milling or Rose turning, they can be a very useful addition to a shop and have many applications.

I want to build a spindle that I will eventually use as a tool post grinder, as is my way I did a fair bit of investigation work into them, I've seen tool post grinders used when I was tool making and I've also seen John's in use, so I had a fair idea what they look like. I also bought a book from the Workshop Practice Series (No 27 Spindles by Harpit Sandhu ISBN-13:978-1-85486-149-8) and found it very interesting and informative, it covers the design and manufacture of various spindles for different application from milling, drilling, grinding and even a high speed spindle to take dremel tooling.

I will be following the design for a "Light weight tool post grinding spindle" modified for my own use.

This is a sanitized sketch of the spindle.



I've collected most of the bits needed together.



The bearing came from Arc Euro Trade £2 each, Johns started the ball rolling by putting a 20mm hole down the middle of the bar, this was a job that would have made my little lathe grunt (thanks John  ) this will eventually become the spindle housing. The housing will be bored to fit the bearings, so I'll need the bore clock, and has I'm going to hold the bearing in place with screwed caps I'll need to do internal and external screw cutting, I could have used adhesive to fix the bearing, but where's the challenge in that, so  I bought some HSS threading tools from Chronos ( just four days delivery including weekend  ), I've still to make a undercut boring bar holder, and I'm waiting for the electric motor that I bought on flebay to be delivered.

So I'm more or less ready to make a start in the next day or two.

Cheers

Stew

[Majorstrain]

Hi Stew,

You've got me interested,

It's one tool that I want to make as well.
What were the specs on the motor you ordered on flea bay?
Iv'e been thinking about a brushless DC and controller as used in electric RC aircraft 

Looking forward to seeing the progress reports.
Cheers
Phil

[sbwhart]

Hi Phil

Its a sewing machine motor 1/8 hp 6000 rpm you don't need a lot of power for grinding you're only taking a lick off.

I'm planing on having two sets of pulley one set giving 4000 rpm for external grinding and one set giving 16000 rpm for internal, thats what I'm aiming for anyway.

Its not arrived yet bought it over a week ago sent vendor a PM today asking where it is, hope its not a scam.

Cheers

Stew

[John Hill]

Stew,   this is very interesting!

I have started on a spindle too and I am interested in your comments re the motor size as I have started to build mine around a router motor, not a big router but a lot bigger than a sewing machine motor! 

I thought that by using the bigger motor and stepped pulleys I could use it as a drill too (for example drilling holes around a diameter in a flywheel or suchlike).

[bogstandard]

To all,

Even though you are normally only taking minute cuts, you do need the grunt there. If you are grinding a fairly large OD, say 3", that is over 9" circumference, it is the constant drag of the wheel that causes the problems. When I grind on my surface grinder say a piece 4" long at 0.0005" (0.01mm) cut, the 1/2 horse motor starts to slow down. So you have a choice, either more grunt to cut thru it, or super fine feeds so there is not as much grinding pressure.

The way to get your very fine feeds is not to use the crosslide for the feed, but the topslide which has been set over a couple of degrees, and the wheel set and dressed square to the job. Grinding angles then becomes a nightmare to set up.

With reference to motors, the original one used on mine (now replaced) was a 1/6th HP free running at 16K.

Bogs

[sbwhart]

Thanks for that John

I was looking for a slightly bigger motor but all I can seem to find is 1/3 HP ish with around 1800 rpm the sewing machine motor is the best I could find, but I'll keep looking, if I find something better, the sewing machine motor will be useful for something, I may even take up sewing.

Cheers

Stew

[Maninshed]

If you are using your spindle as a tool post grinder, a thing to be careful with is the bearing preload, I assume you will be using angular contact bearings, as these are better for this type of work they take the axial and end loads better. I built the quorn cutter grinder type spindle, looks very similar to your sketch, but it has a bearing preload system using springs giving about 10lb preload on the bearings. I would think  the book you have will make some referance to preloading bearings.

Martyn

[arnoldb]

Stew, very interesting.  I'll be closely following this one 

Cheers, Arnold

[sbwhart]

Martyn

I'm going to use ball bearings. Like you I thought taper bearings would be better, from the book the author discuses the use of the Quorn spindle that he thinks is excellent: however, it is best in one direction due to the pre load which is fine for the Quorn, but his spindle could be used in either direction, the author does admit that his solution is not ideal but its simple design makes it easy to manufacture and will allow the bearings to be replaced if undue wear accures.

In his design of what he calls his basic spindle that can be used for milling he uses three bearing a plane bearing at the back and at the front he uses a pair of radial and axial load bearings back to back to take the loads. (I think these are similar to wheel bearing in a car but i'll stand to be corrected on this)

I have looked at the Quorn with a view to making one how have you found it ?, would it be possible to post a few pics so the chaps have an idea what they look like. 

Cheers
 
Stew

[NickG]

Stew,

I would have thought taper roller bearings would be ok to deal with axial and radial load. But maybe ball or roller bearings along with thrust bearings would be better still.

I thought car wheel bearings were taper roller ... not sure ... I know mine need doing though!

Nick

[Maninshed]

Hi Stew.
Angular contact bearings are not taper roller bearings, they look similar to a ball type standard bearings. A standard deep groove bearing if you try to push the inner race laterally out of the outer race (finger pressure) in either direction you cannot. However with an angular contact bearing if you do the same there is some detectable lateral play between the inner and outer races, the idea of the preload is to take this out. The races on an angular contact bearing (sometimes there called magneto bearings) are not a compete 'C' shape there are like half a 'C' in opposing directions, therefore the loading angles are different so they can take tangental loads better. I think the type of bearing you use is more critical if you are going to make a high speed spindle for grinding eg tangetal loads as on the perifery of a wheel, or a milling cutter, if the spindle was for lateral loads only eg drilling I guess you could use a standad deep groove bearing. I hope you can understand my drivel, I just copied the quorn spindle out of the Quorn book. I only lurk on this site at the moment, so have not figured out how to do the photos & attachments yet.

[Maninshed]

NickG.
Its down to the RPM rating on the bearing, taper roller bearings can go up to about 9,000rpm a standard deep groove bearing can get up to 80,000rpm and the angular contacts can be up to 28,000rpm obviously these max speeds depend on size. Another problem when designing a high speed head is making it compact the footprint of a taper roller is quite big compared to a standard or angular contact bearing.

[Darren]

Cars wheel hubs mostly use taper rollers (I think we can agree they can quite take some side and axle loads), my mini lathe now has tapers and my Smart and Brown has a pair of ball races at the front, great big ones that i hope I'll never have to replace and a taper at the back.

The best bit about tapers is you can fine tune the pre-load. But you can over do it as well and ruin the bearing quite quickly.

My pillar drill has one thrust and one roller at the nose and two rollers at the other end.

[bogstandard]

You might find that car wheel bearings on trialing arm vehicles have gone away from the tapered type to just plain ball bearings.

At one time you could tweak them up and regrease them as well, they would most probably last the life of the car. My car is now 7 years old, and it is now showing signs it needs the rear bearings doing again, last replaced 3 years ago.

Do you honestly think car manufacturers nowadays will make something you can easily change or fix yourself. I could do it and most probably you people could as well, but the average man in the street who would normally have tweaked them up himself, is now forced to pay a couple of hundred squid to get them replaced at their dealership.

With regards to Stews bearing dilemma. I have made a few spindles in my time, and personally, I think the standard bearings he has are plenty good enough for what will be a little used grinding spindle, as long as care is taken in getting the spacer the correct length so that the bearings are not stressed, but running perfectly central when the shaft is tightened up. Pre loading shouldn't be required for what he is doing.

For a more dedicated type of a machine like the Quorn, then yes, make a proper preloaded spindle.


Bogs

[Raggle]

It's worth remembering that the Unimat SL headstock uses E-13 magneto bearings. Preload is set by the length of the spacer tube between them and a pair of belville washers.

Plenty of SLs have been doing good service for 40-50 years with widely varying loads and I doubt many owners have replaced these inexpensive bearings more than once, if at all. Offhand I'd say they were good for speeds in excess of 6,000 rpm. The Unimat cartridge is 35mm diam which is not over large considering it has a rack and a keyway. Not too difficult to duplicate.

There'll be a drawing of it somewhere on the Yahoo site

http://finance.groups.yahoo.com/group/UNIMAT/

Arc Euro carry E-10s at £6.50 each and angular contact from £6 a pair

http://www.arceurotrade.co.uk/Catalogue/Bearings/Angular-Contact-Ball-Bearings

HTH

Ray