Which type of bearing to use?

[Inspector]

There are versions of those kind of hollowers made from aluminium although I think they are using stronger alloys like 6061-T6 as a minimum. Steel is still much better and usually cheaper.

You can get hollowers in the UK. Searches will reveal more.

https://hopewoodturning.co.uk/lathe-accessories/jigs/hope-easy-hollowing-jig/?p=1
There are plans available for them and the ones that fit through a gate. I think you'll have to join them and possibly pay a little for the plans. I don't know for sure.

https://www.homemadetools.net/homemade-articulated-hollowing-tool-4
https://www.homemadetools.net/homemade-hollowing-tool-2
A full disclosure of what you were making would have resulted in more specific recommendations. Also posting in the wood turning section or the metal working sections would have been more conducive to getting answers from people that have them.

Pete

 

[Inspector]

A specific search for plans led to a couple more and that doesn't include all the YouTube ones.

http://www.rocky-roost-woodturnings.com/wood-turning-blog/home-made-articulating.html
https://www.homemadetools.net/homemade-articulating-arm-hollower
Pete

 

[bertterbo]

Wrong ones those sit on the top and bot you need these that fit within the middle bar then the top and bottom bar will revolve around the bearing.
Have a look at these: HK0808 INA Drawn Cup Needle Bearing - BearingBoys

Edit: And I would go with steel bar less flex you don't want the ally flex to rip out chunks of your turning.

Yep, if you read the first post, I explained why I was thinking about thrust bearings as they're much easier to apply without having to drill large accurate holes.

I'll have a look at the ones you linked, but not sure I understand how you would use them in this scenario?

 

[bertterbo]

There are versions of those kind of hollowers made from aluminium although I think they are using stronger alloys like 6061-T6 as a minimum. Steel is still much better and usually cheaper.

You can get hollowers in the UK. Searches will reveal more.

https://hopewoodturning.co.uk/lathe-accessories/jigs/hope-easy-hollowing-jig/?p=1
There are plans available for them and the ones that fit through a gate. I think you'll have to join them and possibly pay a little for the plans. I don't know for sure.

https://www.homemadetools.net/homemade-articulated-hollowing-tool-4
https://www.homemadetools.net/homemade-hollowing-tool-2
A full disclosure of what you were making would have resulted in more specific recommendations. Also posting in the wood turning section or the metal working sections would have been more conducive to getting answers from people that have them.

Pete

Thanks. I'm aware of the Simon Hope one and the gate ones, but this one is different. And I had looked for guides on how to make one, but none of the ones I cam across used bearings, which was why I came here to ask.

 

[Bob Chapman]

That's exactly what it's for ..although not for "deep deep" hollowing .. just small project hollowing. It's more to hold the tool for me as I suffer from a bad back (I'm copying the Trent Bosch Stabilizer). I'd be happy to buy one, but he doesn't ship to the UK, so am trying to make one.

The bearings you're referring to sound like thrust bearings, which is what I mentioned in the first post.

Can you post some pictures of your setup?

My setup is made of mild steel. The large sections are 30mm square, the thinner links are 30 x 8mm. From the toolpost end the sections are 250mm, 200mm and 150mm long with 35mm overlaps between sections. The overall length is 540mm at full stretch.
The 'exploded' joint shows the arrangement. The thrust bearings go either side of the 30mm bar, between it and the thinner bars. The threaded rod is 12mm as are the holes through the bars. The thrust bearings are 30mm ouside diameter and 17.5mm inside diameter. To prevent them sliding about I made some spacers from some acrylic 'pen plastic' I had around the place. Altogether there are five bearings in the rig (only one at the top of the toolpost).

Hope this helps

 

[bertterbo]

Excellent, thanks!

 

[bertterbo]

Was it just Mild Steel? or Bright Mild steel?

 

[throbscottle]

I'd take a punt on the one in the photo being a machined pin that's completely smooth. You can see 1 grub screw in the photo. I'd think it was fixed solid somehow into the lower half of the middle section, which is how they get minimal play, combined with a precise fit. Then the top arm grub screw only needs to hold it in place, no need to be particularly tight.

So I'd start with a hss bolt with a plain shank and drill the hole to fit the shank precisely as possible. File around the shank a bit if needed, rather than go the other way. Adjust the thickness of the outer arm with washers so the top surface is a very near fit to but still lower than the bolt's shoulder (or, cut the thread a bit further) then clamp it up tight. All the tension will then be on the thread of the bolt. You could pad it with a wavy washer to fill the last little gap.

For extra cleverness points you could make a sleeve that can go through the outer section and the bolt goes through that. If the sleeve is slightly longer than the hole, it can take all the load and clamp the other middle bar.

 

[bertterbo]

This is how the commercial ones work. There is a bearing seated in a blind hole, on the top and bottom of the middle bar.

A washer then sits on the bearing (top and bottom) to space the top and bottom bar off the middle bar and allow them to rotate freely. A bolt then goes through with a lock nut (didn't mean lock washer in the image) holding it all in place.

The grub screw you are referring to is there to allow the bearing to be removed/replaced I think.

 

[Bob Chapman]

Was it just Mild Steel? or Bright Mild steel?

BMS now you remind me.
There's no play in the arrangement, it works very well.

 

[Fergie 307]

That's exactly what it's for ..although not for "deep deep" hollowing .. just small project hollowing. It's more to hold the tool for me as I suffer from a bad back (I'm copying the Trent Bosch Stabilizer). I'd be happy to buy one, but he doesn't ship to the UK, so am trying to make one.

The bearings you're referring to sound like thrust bearings, which is what I mentioned in the first post.

Can you post some pictures of your setup?

View attachment 154209

I have has similar issues with US sellers unhappy to ship to the UK. May be worth asking if anyone here who lives on the other side of the pond would order it for you and then send it on. Have done that a few times on other forums.

 

[Phill05]

Yep, if you read the first post, I explained why I was thinking about thrust bearings as they're much easier to apply without having to drill large accurate holes.

I'll have a look at the ones you linked, but not sure I understand how you would use them in this scenario?

Sorry for the delay responding to you I did read your first post and that is why I suggested using the needle rollers as they are designed to do just that job I have paragraph arms on engraving machines that work just like this and they were designed in the UK:


You want something EASY to do right?

Drill a 10mm hole through square bar then open up to 12mm wide x 10mm deep at each end to hold the needle rollers.

Drill a 8mm hole through both flat bars to hold a 8mm shaft and file a flat on each end then put a grub screw in each side to hold on the flats on the shaft too hold in place put two washers in between to reduce the drag.

No machines to use just take measures from bearings mark out correctly then using a hand drill this job could be done within the hour sit back with a pint in your hand and say it works.

Edit: just remembered file down the 8 mm rod flush to top and bottom bars so when you are using there is no projections to catch on unlike your bolt through.

 

[bertterbo]

Sorry for the delay responding to you I did read your first post and that is why I suggested using the needle rollers as they are designed to do just that job I have paragraph arms on engraving machines that work just like this and they were designed in the UK:

View attachment 154317
You want something EASY to do right?

Drill a 10mm hole through square bar then open up to 12mm wide x 10mm deep at each end to hold the needle rollers.

Drill a 8mm hole through both flat bars to hold a 8mm shaft and file a flat on each end then put a grub screw in each side to hold on the flats on the shaft too hold in place put two washers in between to reduce the drag.

No machines to use just take measures from bearings mark out correctly then using a hand drill this job could be done within the hour sit back with a pint in your hand and say it works.

Edit: just remembered file down the 8 mm rod flush to top and bottom bars so when you are using there is no projections to catch on unlike your bolt through.

Thankyou for the idea, but this is basically what I already described in the first post. The problem is that for the bars to move freely, you have to have a little spacing (play) where you have the washers. And even the smallest amount of spacing makes the whole thing jiggle about (you'd be surprised!). The friction of the dowel isn't the issue. It's the friction of the bars I am trying to overcome, which was why I asked about thrust bearings.

 

[J-G]

Thankyou for the idea, but this is basically what I already described in the first post. The problem is that for the bars to move freely, you have to have a little spacing (play) where you have the washers. And even the smallest amount of spacing makes the whole thing jiggle about (you'd be surprised!). The friction of the dowel isn't the issue. It's the friction of the bars I am trying to overcome, which was why I asked about thrust bearings.

Regrettably, I suspect that you are on a hiding to nothing.

Your first post tells me that you don't have the equipment which would enable you to come even close to 'Zero Play' - M8 bolts will not be 8.00mm dia. so will never be suitable.

You could try Nylon or Delrin washers which might eliminate some of the freedom but you'll still have a massive amount of 'play'.

To use either Needle Roller or Needle Thrust Bearings will require high precision machining. - - - - - Here are some accurate drawings (@Phill05 has done a good job of showing the concept) - - - -

This shows an 8 x 12 x 12 standard Drawn Cup Shell type Roller Bearing - to use this you would need to accurately 'Bore' (not 'Drill') or at least Ream the 12mm dia. holes 'in-line' from opposite sides. Though you could ream straight through and fit a loose spacer between the bearings.

Without using inner rings there is nothing to clamp up to so you would need to find some way to restict the clamping force of whatever nuts/washers you use - - - double nuts might work.

A slightly different aproach - with vastly superior 'play elimination - would be to add Needle Roller Inner Rings but this needs more accurate machining so that the 'Inner Rings' clamp solidly with the outer bars leaving as little as 0.1mm clearance. Again, adding Nylon or Delrin washers could be beneficial.

The drawing shows 10 x 12 x 10 Bearings with 8 x 10 x 11 Inner Rings.

Thrust Bearings would demand the most sophisticated machining facility and have other negative attributes.

This shows 8 x 21 x 4 Thrust Roller Bearings which have 1mm thick thrust plates - making the total height 6mm.

I can't be certain (since I don't have any thrust bearings on the shelf to test!) but I suspect that even if you used double nuts to control the amount of 'Pre-load' you would still be more prone to 'play' - you certianly would if using standard M8 bolts.

I haven't shown any nuts or washers since they are secondary considerations to the main problem of eliminating 'play'.

 

[bertterbo]

Thank you for taking the time to make up drawings. I'm currently just going to go with the thrust washers as per Bob Chapmans post as it requires the least precision, and means I will have no vertical play (which is all that matters for my use case)

 

[J-G]

Thank you for taking the time to make up drawings. I'm currently just going to go with the thrust washers as per Bob Chapmans post as it requires the least precision, and means I will have no vertical play (which is all that matters for my use case)

You're welcome - I know I was a bit late in replying but I didn't think anyone had picked up on the lack of suitable machinery or skill really involved to do a 'proper' job.

I hope your efforts are successful and you do find an acceptable level of freedom along with rigidity.

Personally, I don't think that what you propose will give you 'no vertical play' - - - but I've been wrong before

 

[Bob Chapman]

BMS now you remind me.
There's no play in the arrangement, it works very well.

"No vertical play" is an absolute. When I claimed no play I meant " not enough to matter". In use the tool is supported by the toolrest in the usual way. Woodturning is not precision machining. The result will still depend on the skill of the turner. This arrangement simply makes it easier. I'll choose my words more carefully in future.

 

[bertterbo]

Also, when I say "No vertical play", I mean specifically between the thrust bearings and their surrounding pieces. I am under no illusion that there will be some play in the jig as a whole. : )

 

[Bob Chapman]

Thanks Betterbro. I think we are singing from the same hymn sheet.

 

[Inspector]

I wonder if a TV mount could be adapted to do the job? This one on sale is $20Cad and as long as it can be loosened enough to move freely and a holder made for the tool shaft I think it would work. I'm not trying to get the OP to change course but it might get the creative juices flowing for someone else thinking about making one.

Pete