B Mandrel and Perfect Fit

[Lenny]

I am working on my first Perfect Fit. It uses the slightly larger B mandrel and the bushings therefore have the larger I.D.

I have glued the upper tube in flush with the cap end creating the space for the centerband and avoiding having to part it off.
My problem is the blanks do not both fit on the mandrel with the bushings ... the last bushing would be over the threads which are the standard mandrel size...

I have resisted turning them between centers for fear of flaring the unsupported tube at the CB. I probably will just turn the cap blank using the mandrel and the lower between centers but I would like to hear what others do.

Thanks!

 

[ed4copies]

Hey Lenny!!

That has been a problem for years!! I resolved it by putting spacers on the mandrel and turning one half at a time.

TODAY, I would resolve it by using a "mandrel saver" tailstock piece (and turning one half at a time). Unfortunately, you would probably have to make this a "dedicated mandrel saver, since I think you would have to drill the hole a little larger to accommodate the "B" mandrel. If you are making five or more pens, the $20 investment is not too bad (IMO).

Hope this helps,
Ed

 

[Lenny]

Thanks Ed! I'm just glad to know it isn't ME!

 

[Joe S.]

TBC with bushings might work.

 

[Mack C.]

I am working on my first Perfect Fit. It uses the slightly larger B mandrel and the bushings therefore have the larger I.D.

I have glued the upper tube in flush with the cap end creating the space for the centerband and avoiding having to part it off. View attachment 87620
My problem is the blanks do not both fit on the mandrel with the bushings ... the last bushing would be over the threads which are the standard mandrel size... View attachment 87621

I have resisted turning them between centers for fear of flaring the unsupported tube at the CB. I probably will just turn the cap blank using the mandrel and the lower between centers but I would like to hear what others do.

Thanks!

I am lucky enough to have 2 sets of johnnycnc's Perfect Fit bushings (14B). They came with a ring to fit over the tube when you have cut the tenon. I see they aren't in his inventory of steel bushings anymore.

 

[thewishman]

I have given up on the mandrel, but don't yet have the TBC bushings for all of the kits. I have used the factory bushings between centers and found (too late, too often) that I must measure constantly - there are a lot of bushings that are not quite right.

For me, it is better to cut the tenon at the end. I was rounding over the end of the blank while sanding and messing up the transition to the centerband.

 

[PenMan1]

Simple fix, Lenny! Since you are using a Beall collet, shorten your B mandrel until the "b" nib bushing extends over the threads 2 or 3 turns. Most of this bushing should still be on the mandrel. Use the washer and 7/16 nut that came with the mandrel.

Using this method (and it's the best I've found), the cap end of PF must alway be loaded toward the headstock and the nib toward the tailstock.

Since you are using my "1 7/8 exposed" method, it is CRITICAL that you use the "5th" bushing in the set over the exposed tube. Besides acting as a "CB measurement" device, IT KEEPS YOU FROM DEFORMING THE EXPOSED BRASS TUBE.

Since PF is one of the few that uses a b mandrel (Woodcraft's A bushings of Cambridge and El Grande work better for me), a different collet than a 7 mm mandrel, you can scratch a mark on the B mandrel, slide the collet to the mark, and store bushings in order between the collet and the 7/16 B mandrel nut.

I've tried a mandrel saver with PF, I had terrible results. It was difficult for me to accurately drill out the 7mm mandrel saver. AND, FWIW, that 7/16 nut comes with that particular mandrel for a reason . IMHO,The bass nut just does work very well for this set up.

I hope this helps.

 

[PenMan1]

FWIW:
Two reasons that I use the "measure the top blank to 1 7/8, square the blank on the sander, glue the tube flush to the cap end of the top blank, and load blank with the "5th" bushing covering the exposed tube" method.

First, it is much easier for me to insure that I have a precise fit at the centerband and keeps me from cutting down the OD of the tube removing paint/epoxy glue. Scuffing the tube ANY on this set results in having to glue the centerband in place.

Second, by NOT HAVING TO load the upper blank without "bushing 5", parting a tenon down to the tube, unassembling the mandrel set up, putting bushing 5 in place to protect the exposed tube, and reassembling the entire blank set up saves a GREAT DEAL of time. Additionally, once you have the blank set up spinning nice and "concentricly, it eliminates one step that could cause issues with this set.

Respectfully submitted.

 

[Lenny]

Andy, if I follow you correctly your saying take the B mandrel out of it's Morse taper and use it with the Collet chuck? By doing so I will gain a little ... allowing the nib bushing to be over the mandrel more?
I did figure out that keeping the sizing collar on the exposed brass was the only way to go!

Joe and Chris ... Thanks, my first thought is always to TBC ...just seems difficult to do the lower blank that way in this case.

Mack, you ARE lucky to have those bushings!

 

[PenMan1]

That's exactly what I'm saying, Lenny. The other option (since I can't find the standard 8mm Mandrel rod, stand alone) is to buy an 8mm (I think it is, but measure) piece of drill rod and THREAD THE #%^+ rod to the closest size you can get to the actual mandrel rod size.

Making your own mandrel rod allows you to not have to "patch" a set up that was factory made to use a "universal" nut that doesn't work with this particular set. As you are finding, I found the "b" mandrel with the taper to be perfectly useless for PF!

Try your Beall (7-8 collet, I THINK). I think it will end all of the jury rigging. BUT, notice that the little washer that came with the mandrel fits snugly on the threads AND is the exact size of the nib bushing. COINCIDENCE? I don't think so

 

[PenMan1]

Turning the bottom barrel of PF TBC IS difficult, but can be done.
Since the bottom bushings use no collar (jams up like slim bushings), the only way I know to TBC is with 60 dead and live centers. To get the blank tight enough to turn flairs the thread connector and the nib fitting, requiring them to be epoxied into place. DAMHIKT!

 

[PenMan1]

I have made so many PFs that I think I have made NEARLY every mistake you CAN make on these.

If they didn't sell so well, out perform the MB Meisterstuck, and were not so simple to customize, I put a bounty on them.

As you are finding. Theses are NOT FRIENDLY for a beginner.

 

[PenMan1]

The problem I had with the B mandrel IN the taper is that the mandrel is so large that it wouldn't go into the taper far enough to get the threads where I needed. After experimenting with using another PF nib bushing between the taper and the clip bushing, I finally just took the rod out of the MT and stuck it in the Beall. I've been a happy camper ever since.

 

[Lenny]

I NEVER lose anything but unfortunatly my washer and nut is on the long term "misplaced" list! :wink:

The problem I had with the B mandrel IN the taper is that the mandrel is so large that it wouldn't go into the taper far enough to get the threads where I needed. After experimenting with using another PF nib bushing between the taper and the clip bushing, I finally just took the rod out of the MT and stuck it in the Beall. I've been a happy camper ever since.

I will try that.

I have made so many PFs that I think I have made NEARLY every mistake you CAN make on these.

Well, I'll let you know on that one! :redface:

 

[chrisk]

Lenny, I had the same problem (the kit doesn't fit properly on the mandrel) and fixed with Johnny CNC's bushings and TBC.

 

[PenMan1]

Lenny, I had the same problem (the kit doesn't fit properly on the mandrel) and fixed with Johnny CNC's bushings and TBC.

If enough of us wanted these, I'll bet he would make them again. These ARE ideal.

 

[Aces-High]

The a mandrel that I have goes into a collet, I wonder if there is one for b?

 

[magpens]

The A mandrel is 0.247" diameter, and I assume you use a 1/4" collet = 0.250".

The B mandrel is 0.291" diameter ... so what collet to use for that ?

Is that the question ?

You could try a 9/32" collet = 0.281" ... that would be forcing the collet open a tiny bit which you are really not supposed to do, but I think it would work ok for that small expansion of the collet. The 9/32" is available ... for example here:

https://www.maritool.com/Collets-ER...56_59/p685/ER32-COLLET-9/32/product_info.html

Alternatively, you could go for a 7.5 mm collet = 0.295", which is available here:

https://www.mscdirect.com/industrialtools/7-sp-46-sp-5-mm-collet.html

or a 19/64" collet = 0.297" which is also available, here :

https://www.maritool.com/Collets-ER..._59/p2531/ER32-COLLET-19/64/product_info.html

Whatever collet you might order would, of course, have to match the collet chuck that you own - ER-32 for the first and third, while ER-16 for the second, as I interpret things.

If you have the Beale collet chuck, I don't remember its specs, but the Beale website or a quick phone call could settle that.

There are some other chuck systems for which the specific collets mentioned may not be available. I think that PSI used to sell a really odd size collet chuck in which only their own collets would work and you would not get any of the 3 sizes of collets mentioned.

I know that a collet is the best way to grip the mandrel, but in the past I have just gripped a mandrel in the headstock chuck jaws and always got satisfactory results. Depends on the runout of the headstock chuck and maybe I just got lucky.

If you have a lathe with a MT2 headstock taper you could buy one of these; although out of stock at BearToothWoods.com presently, it must be available somewhere and will do the job admirably for you:

https://www.beartoothwoods.com/catalog/product_info.php?cPath=42&products_id=105