turning between centers

[dcannon]

Hello All,

I've been having some out-of-round and finishing issues that have led me to try turning between centers rather than on the mandrel. I've been looking at a lot of the threads on "mandrel less" turning, but still have one question that I want to make sure I understand. If I simply have a 60 degree dead center as the drive and a 60 degree live center in the tailstock, do I need the special bushings that have the 60 degree dimples in the ends, or is it possible to use the standard bushings that I was using on the mandrel with the dead and live centers inserted into the ends of those?
OR, are there any other drive-center ideas that work better with standard bushings, rather than the 60 degree dead that I'm thinking of using. Thanks for any help you can offer!

Dan

 

[WoodNutOntario]

Dan,

You can use the standard bushings that come with the kits although they are not the best quality and they will most likely give you a lot more problems than they are worth.
I use some of my syandard bushings with this technique and it works out really well. Others it just messes up the pen and i get seriously out of round tubes.
Johnnycnc has the correct bushings to use, or if you are proficient with a metal lathe you can make your own sets of bushings.

Turning between centres is a great way to turn, but as with everything else relating to this hobby you need to have the correct tools and accessories to make it successful.

Andrew

 

[aggromere]

Sometimes the out of round is because of the bushings. The original bushings sometimes are not drilled exactly in the center or may be slightly out of round. You can use them, but if they are bad, you will still get out of round results. I also suggest you pick up a set of TBC bushings from JohnnyCNC.

Just like you say use the regular dead center that is 60degrees and get a 60 degree live center for the tailstock.

 

[rej19]

I agree with both of the guys above. You can use standard bushing but there is a sometimes a significant quality difference between standard bushings and Johns bushings. I would suggest turning a couple of expendable blanks with what you have and see how well the bushing perform. I have found with some of the cheaper bushings there are differences from one set to another even though they are the same manufacturer. You won't find that with Johns bushings. His are very well made and consistant. If you going to be turning a lot of pens they are well worth the investment.

 

[1nfinity]

If bushings aren't to fault in your out-of-round issues, another approach might be to try PSI's Maxi-Madrel in conjunction with a 60 degree live-center in the tailstock. I adjust and shorten up this mandrel, using it to turn one blank at a time. With this shortened turning length there is less flexure, more rigidity, and greater stability. The out-of-round problems I was encountering were eliminated using this approach. If this method had failed, the next approach would have been to turn between centers per Texatdurango's 2010 library article Turning Between Centers.
If you're interested in the Maxi-Mandrel, you can find it at the following link:
http://www.pennstateind.com/store/PKM-FLC.html

Terry

 

[Mr Vic]

I turn my blanks with bushings and mandrel till Im near the diameter. Then I'll dismount and finish w/o bushings between centers. I use a micrometer to determine correct diameterr for the fittings I'm using. I don't use a metal dead center. I tapped a block of UHMW plastic which screws onto the drive spindle. With a skew I turned it down to 60deg. I like it because it has some give which reduces the chance of tube flaring. If it gets gunked up I just turn it down a bit more.

 

[dcannon]

Thanks for the replies everyone. There are some good ideas here that I might give a try. I was hoping I might be able to give the TBC approach a shot without any kind of cash investment (although the bushings from JohnnyCNC are certainly reasonable), but of course that's usually wishful thinking :biggrin:. At the very least, I may try my existing bushings first just to see how it goes and as they wear out I'll probably end up replacing them with Johns.

Mr Vic, I kind of thought of something like that, but don't have a way to tap it for the spindle, I was thinking maybe I'd used my chuck to hold it instead. I'll be doing some experimenting and let you all know what I end up doing. Thanks again.

Dan

 

[TerryBlanchard]

Heat can cause out of round blanks as well. It is not always the bushings causing the problem. Caution as to not getting the blank too hot when turning, stop from time to time and let things settle down and go again.

 

[avbill]

$ investment is a concern, If you decide to go TBC buy one kit bushing at a time over a period of time you will have all the bushing that you turn. you do not need every one a the moment.

 

[markgum]

I'm thinking about getting one of these. I could probably get the parts at Lowes or HD, but.. http://cgi.ebay.com/Lathe-Spindle-Runout-Gauge-wood-pen-turning-tool_W0QQitemZ200552041785QQcategoryZ42282QQcmdZViewItemQQ_trksidZp5197.m7QQ_trkparmsZalgo%3DLVI%26itu%3DUCI%26otn%3D4%26po%3DLVI%26ps%3D63%26clkid%3D5573728689254933188
with the price might be worth it.

 

[Spencemark]

sometimes the 60 degree live center gets worn and the bushings don't seat correctly. Check to see if there is a wear ring on the end of the center. A hardened center is better but might be a little more expensive to buy.