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View Full Version : What kind of bearings?



srn4 - n/a
1-Apr-06, 12:16 PM
There are so many different types and makes of pillow block bearings, im getting confused and worried I will buy the wrong thing again....



Can anyone sugest a suitable super strong bearing and a good supplier because the ones I have are useless because they have play in them and are giving me cause for concern.



I need a pair for the lower fan shaft on my craft (25mm shafts)



you can see photos of the shaft here:

http://www.tegwin.demon.co.uk/Craft%20assembly%202%2003%2010 (www.tegwin.demon.co.uk/Craft%20assembly%202%2003%2010%2005/Viper%20093.jpg) %2005/Viper%20093.jpg



http://www.tegwin.demon.co.uk/Craft%20assembly%202%2003%2010 (www.tegwin.demon.co.uk/Craft%20assembly%202%2003%2010%2005/Viper%20101.jpg) %2005/Viper%20101.jpg



Sorry for all the short questions recently, I am pushing to get this thing finished now http://hovercraft.org.uk/images/icons/smiley_icons/icon_cool.gif



Dunc

Paul Fitz - n/a
1-Apr-06, 02:06 PM
All bearings will have some play in them! If you are not happy with the ones you have (Chinese if I remember correctly) contact any of the major distributors and ask what they can offer.



For many years I used BSL Ltd (Now Brammer-BSL) with no problems.

http://www.brammer.biz/uk.aspx



there are others e.g. http://www.midlandbearings.com/



Or you could contact one of the major players direct although you would probably have to purchase from a distributor.

http://www.skf.co.uk/

srn4 - n/a
1-Apr-06, 02:22 PM
I seem to recall you mentioning back then that Chinese bearings where not perfect.



My problem is that when I rev the engine hard the lower pulley is pulled upwards a little bit and I want to try and correct this.



I think my design is less than amazing, but I was hoping some better bearings might compensate a bit.



Dunc

Ian Brooks - n/a
1-Apr-06, 04:11 PM
Dunc



It may not be the bearings that have play... if that was the case, you would expect the play to be taken up at low speed/loads, but you think this happens at high load/speed.



You have both bearings very close together. As the fan speeds up, the belt tension gets higher, and this is reacted via the shaft by the pair of bearings.



Assuming that the bearing centres are say 30mm apart, and the shaft is say 90mm, then the load on the bearings is 3x the tension on the belt.



High bearing loads will cause the bearing mounts to deflect, allowing the shaft to deflect upwards possibly causing the effect you are seeing.



It may be that you need to stiffen the bearing mounts up? Or ideally move the bearing centres further apart.



Ian



PS - I notice the red square tube is bolted via bolts passing through the tube. These probably wont create enough clamping force, so the bearings will move in time. Can it be welded?

srn4 - n/a
1-Apr-06, 04:18 PM
Hi Ian.



I think we talked about this before, and according to some rather clever maths in theory they should be far enough appart http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif



However, I guess I misjudged one of the variables quite dramatically http://hovercraft.org.uk/images/icons/smiley_icons/icon_confused.gif



I might as well try moving one of the bearings back slightly....Currently the centres are 45mm, I recon I can get another 25 without having to take a grinder to the entire craft...



Will have to see if that works before I go ahead and get new bearings.



At the moment I have one bearing the right way up and one upsideown, will this cause any problems?

lazza - n/a
1-Apr-06, 09:24 PM
Sorry for all the short questions recently, I am pushing to get this thing finished now http://hovercraft.org.uk/images/icons/smiley_icons/icon_cool.gif



Dunc




I'm going to email your mother Duncan and tell her to whack you around the legs with a broom stick each time she see's you rushing the last part of the build http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif Just remember that rushing can lead to shortcuts that arn't always the best choice http://hovercraft.org.uk/images/icons/smiley_icons/icon_sad.gif

srn4 - n/a
2-Apr-06, 12:33 AM
I keep telling myself that Lazza.... Its taken me just over a year to get this far..another month to get things right is nothing http://hovercraft.org.uk/images/icons/smiley_icons/icon_confused.gif



I just dont want to miss the entire season like I did with the last craft.





I think I have come up with a solution to my probelm, I just have to do some hacking and welding for a couple of days and hopefully things will look better!



Other than that, its just the skirt to go http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif



Dunc

jon_curtis - n/a
2-Apr-06, 07:15 PM
have a good think about how you build up that back welded bearing mount! if you go back further build in some kinda angular bracing to support against the frame uprights, maybe weld some 45 deg. gussets in out of 3mm plate for example. which would be nessesary, if you say welded some 2x1" tube on its side along the back to get the bearing further back!



jon



ps. your not running at full speed with a loosey fitted or no guard fitted are you? dont facey a load of flying plastic in your face, if something fails?

richardevans - n/a
5-Apr-06, 04:03 PM
Dunc,



I had this very problem. I agree with Ian and Jon.



The force on the lower shaft might well be distorting the fan frame a little, and it only takes a bit of movement in the frame to give an amplified movement at the pulley - the 3x effect.



Have a look at the pictures on my website:



http://www.rhevans.co.uk/january2004.htm



to see the extra diagonals I added on to brace it properly.



http://www.rhevans.co.uk/bottom_pulley_in_frame_200h.jpg





Regards,



Richard E.

srn4 - n/a
5-Apr-06, 05:00 PM
Thanks Richard.



I have now done some hacking and welding, and although it is proberably excesivley strong and heavy now Im happy that it might work a little better.





Will post some photos tommorow when im not stuck inside doing paperwork http://hovercraft.org.uk/images/icons/smiley_icons/icon_mad.gif