The_Bird_Man
Apprentice Member
I assume you mean the bushes on the mandrel ? But how can this be. It's brand new. Also how do I turn between centers with/without bushes ? Many thanks, Eddie :)
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Help Please ! :)
- Thread starter The_Bird_Man
- Start date
Eddie, you are drilling to 7mm, you are using a 7mm barrel trimmer, and therefore presumably you are using 7mm bushes. In which case, you can discount the bushes as being the cause. 7mm bushes, as of course you already know, don't enter the tube, and therefore cannot be held responsible for the tube being mis- shapen, as shown in your photo.
When you say you trim using a pillar drill, are you just using the drill to hold and rotate the trimmer, then offering the blank to the trimmer by hand, or are you holding the blank in some sort if vice, then lowering the chuck for the trimmer to enter the blank tube?
When you say you trim using a pillar drill, are you just using the drill to hold and rotate the trimmer, then offering the blank to the trimmer by hand, or are you holding the blank in some sort if vice, then lowering the chuck for the trimmer to enter the blank tube?
The_Bird_Man
Apprentice Member
Hello Phil, that's correct, all 7mm :) Yeah I've built a little right angle jig with base and hold the blank with a clamp flat to the sides lowering the chuck :)
The_Bird_Man
Apprentice Member
I do apologies, I should of mentioned the size of the bushings and tubes I'm using. I also forgot to mention I did a bounce test too, perfect, very smooth and true.
I suspect Eddie, it has something to do with the relationship between your jig and the trimmer in your drill, and whichever one is at fault you can easily overcome it with one simple adjustment to your method.
Abandon the jig!!
Keep the drill revs down to about 2 to 3 hundred, and just hold the blank by hand. Instead of lowering the chuck and trimmer into the tube, push the tube by hand onto the trimmer. The trimmer shaft will keep it square, so you don't need a jig to do it for you.
I suggest your problem is nothing to do with lathes, bushes, mandrels, spindle alignment and so on - I suggest you are mounting on your mandrel, a tube that is already mis-shapen, because you have distorted it in the process of trimming. The tube on your photo is clearly not round, and therefore your chances of turning a round pen barrel are extremely slim to say the least.
Give it a go without the jig and see if it makes a difference. You could just as easily put your trimmer in a jacobs chuck on the lathe and push the tube over the trimmer that way, which is what many, many people do. Its the same principle, but in both cases it's the trimmer shaft which keeps the whole thing true not an over reliance on engineering micro-details by attempting to in marry a jig to a drill in 3 planes.
Abandon the jig!!
Keep the drill revs down to about 2 to 3 hundred, and just hold the blank by hand. Instead of lowering the chuck and trimmer into the tube, push the tube by hand onto the trimmer. The trimmer shaft will keep it square, so you don't need a jig to do it for you.
I suggest your problem is nothing to do with lathes, bushes, mandrels, spindle alignment and so on - I suggest you are mounting on your mandrel, a tube that is already mis-shapen, because you have distorted it in the process of trimming. The tube on your photo is clearly not round, and therefore your chances of turning a round pen barrel are extremely slim to say the least.
Give it a go without the jig and see if it makes a difference. You could just as easily put your trimmer in a jacobs chuck on the lathe and push the tube over the trimmer that way, which is what many, many people do. Its the same principle, but in both cases it's the trimmer shaft which keeps the whole thing true not an over reliance on engineering micro-details by attempting to in marry a jig to a drill in 3 planes.
The_Bird_Man
Apprentice Member
Ah ha !! I shall give that a try tomorrow, thank-you !!! I'm not questioning you so please don't think I am, I just don't quite understand it. Even if the tube is not 100 % round, lets say a fraction out, as in the tiniest amount, would that really cause this much of a problem ? Eddie.
As in the tiniest amount? The problem will be in proportion to the degree of tininess.
To what extent can you guarantee the accuracy of your jig? Even if you can guarantee that both jig and trimmer are 100% vertical, if the jig is out laterally by even a quarter of a millimeter, because your tube and blank are held rigidly in your jig, that error is transmitted down the entire length of the tube, and you will have a tube that is oval not round.
Hold the blank by hand, and even if you mess up at the point of entry, the error will only be at the point of entry - the shaft will straighten things up because your hand is not a rigid platform. Therefore the length of the tube will still be round.
The end of the tube in your photo is getting on for square, suggesting that the relationship between your your jig and trimmer is inaccurate both vertically AND laterally.
Abandon the jig - you don't need it. I believe it is the root of your problem.
Please don't think I'm criticising your ability to build an accurate jig. It could just as easily be the accuracy of the drill that is at fault. It's the relationship between the two that is the problem, but either way, it is overcome by losing the jig.
To what extent can you guarantee the accuracy of your jig? Even if you can guarantee that both jig and trimmer are 100% vertical, if the jig is out laterally by even a quarter of a millimeter, because your tube and blank are held rigidly in your jig, that error is transmitted down the entire length of the tube, and you will have a tube that is oval not round.
Hold the blank by hand, and even if you mess up at the point of entry, the error will only be at the point of entry - the shaft will straighten things up because your hand is not a rigid platform. Therefore the length of the tube will still be round.
The end of the tube in your photo is getting on for square, suggesting that the relationship between your your jig and trimmer is inaccurate both vertically AND laterally.
Abandon the jig - you don't need it. I believe it is the root of your problem.
Please don't think I'm criticising your ability to build an accurate jig. It could just as easily be the accuracy of the drill that is at fault. It's the relationship between the two that is the problem, but either way, it is overcome by losing the jig.
wm460
Grand Master
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- Mar 16, 2013
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Very interesting reading Walter thanks for posting.
The_Bird_Man
Apprentice Member
Barrel trimmers are horrid little things IMO. Get yourself set up with a disc sanding jig and you'll never look back and if you do it'll be absolutely square - as long as you set it up square to begin with ! Another benefit is that you won't rip the end of your blanks when the blades dull. To get the best out of the disc set up it pays to get a set of transfer punches as well
Penpal
Grand Master
Caution using barrel trimmers I only use them by hand most protude being longer than the brass therefore putting your other hand in line for an unexpected hole and without the feel necessary for accurate estimation of how aggressive these beasts are so many blanks are ruined this way especially our burled and tough timbers. A sanding disk can be your best friend.
Carrying out so many checks and balances has been a marvellous introduction to pen making these problem solving methods will become second nature and able to contain the hobby within boundaries. Have fun mate.
Peter.
Carrying out so many checks and balances has been a marvellous introduction to pen making these problem solving methods will become second nature and able to contain the hobby within boundaries. Have fun mate.
Peter.
Penpal
Grand Master
OLive and Amboyna blanks squared and reamed with a whisker of reaming acheived by using a disk sander for square flattening and a form of hand reamer that clears and cleans the inside of the brass another step in the future using easy to prepare blanks however they are not the normal for me most blanks I cut to follow the grain so the aim is to flatten the blank in relation to the brass.
Peter.
Peter.
Attachments
The_Bird_Man
Apprentice Member
Hi all !! Apologies for not responding for a few days, had a bit of trouble with my laptop and had no access to internet. Anyway, after reading the suggestions I built myself a disc sander on the lathe and also built a jig to make it easier to get it square. Now doing this has allowed me to test how square the ends really are by using a try square. I've got them pretty dam square, no light passing through the blank and square, but unfortunately I am still producing concentric blanks. I'm at my whits end as to what I'm doing wrong 
So tomorrow I'm going to have a go at what Pierre suggested, turning the blanks 1/4 of a turn during turning. Quick question, how does this work ? Many thanks Eddie ! :)
So tomorrow I'm going to have a go at what Pierre suggested, turning the blanks 1/4 of a turn during turning. Quick question, how does this work ? Many thanks Eddie ! :)
You've got squared blanks, you've checked the alignment of your head and tail stocks, you've checked that you're mandrel is true, you say you are not over tightening the nuts on the mandrel - frankly there's not a lot left to check. However, SOMETHING is causing the problem. Have you compared the i/d of your bushes to the o/d of your mandrel?
I have the same issue, and the mandrel is 6.13 and the bushing I measured was 6.25 approx. The quarter turn can work a little but doesn't seem to 100%
It's a pain in the a***, I check everything regulary ...
Your mandrel is undersized as all the one I have measured are 6.24 mm
The_Bird_Man
Apprentice Member
Hello all again !!! Apologies for the very delayed reply !!!! Hope everyone had a merry Christmas and a good new year ! :) Got round to being back in my little shed and having ago at pen turning again. Unfortunately the problem still persists :( It's getting better which is good but I still get it where when it come to assemby the join isn't flush all away around. I have included a picture. Reading Bellringer's comment my mandrel seems to be undersized too. It measures 6.14 mm, the internal measurment of the bushings is 6.22 mm and the internal measurments of the brass tube is 6.24. I can only think that it must be that !! I was thinking is there anyone on here I could also purchase a pair of blanks pre drilled, glued and squared just to be certain it's not down to an error of my preperation, haha ! Many thanks Eddie :)
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Penpal
Grand Master
From the picture mate the end facing is pretty rough the turned piece is out of round two ways I am fairly sure there are members plural in your area of Lincolnshire someone could come to your rescue perhaps. Is there a wood group in your area?
Peter.
Peter.
Welcome Eddie
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