Barrel Trimmer Issue?

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BTS

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Duluth, Minnesota
I square my pen blanks using a barrel trimmer mounted in the tail chuck on my lathe. After I turn the pieces to shape, I notice on the ends of the pieces that the grain of the wood isnt cut cleanly, but rather is bent over at like a 45 degree angle (see how the fibers are bent over at both ends of the piece in the
pen barrel.jpg
photo). When I apply mineral spirits to clean off the dust, or as I have noticed on past pens, that where the fibers are bent over, that it leaves a dark ring that is quite obvious and distracting/bad.

My barrel trimmer is sharp (as far as I can tell), so what, if anything, am I doing wrong? lathe speed wrong? advancing the cutter too fast with too much pressure? Or is this just the nature of the beast with barrel trimmers and it is unavoidable?

Thanks!
Matthew
 
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I don't know the reason. . But I have a question or two.

Firstly, is that black line a crack ? . That thought caused me some alarm because it looks like a crack in your pic.
There even seems to be a shadow from one side being higher than the other.

Secondly, YES, I can see the end fibers bent at about 45 degrees ... that's alarming also ... a good sharp end mill should not do that.
I assume you have a brass tube in your blank and that the shaft of the end mill is a good fit to the I.D. of the glued-in brass tube.

And I am puzzled that your pic seems to show two blanks ... is that right ? . Are you using a mandrel to support the blanks ?
You should really do the end milling to one blank at a time.
( Maybe your pic does not show the end mill ... so I might be jumping to the wrong conclusion here. )

As an experiment, instead of the end mill, could you try a very sharp skew chisel to trim the end of a drilled & tubed hardwood blank.
Of course, you have to support your skew with the tool rest adjusted appropriately ... going across the lathe bed.
A lathe speed of up to 1000 should be OK. . Use a test piece of wood which has been drilled to 3/8" ( and tubed ) just to try this out.
The blank should be held securely in your headstock chuck ... or ( better ) in a collet chuck of the correct size.
I assume what you will get ( if the skew chisel is sharp ) will be a nice clean cut without that "45-degree problem".

That's what you should get with the end mill also, if you are using the correct size of shaft in the end mill, and assuming mill is sharp .
 
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A number of things could cause it, IMO. Lack of sharpness and or angle of sharpened edge (incorrect angle); End grain cutting can always be iffy. I would guess - it was not sharp enough and too much pressure combined with the particular end grain wood.

Is it a carbide barrel trimmer or steel?
Steel dulls quickly and the faster the quicker it will dull and burn the wood.

The wood should not be burning either.

There are a number of different barrel end sanders and many of the long term experienced ones will use these to bring to correct length and square it up at the same time. Barrel Trimmers work but can do damage quickly when not expecting it.

Look up Rick Herrell's "Off Set Sanding Jig" and way down the page the "Sanding Mill 2.0".

"Custom Made" penturning tools/accessories

This thread is Closed. But here's the link to my New PDF catalog. https://www.penturners.org/threads/ricks-custom-made-tools-pdf-catalog.180009/
www.penturners.org

I have the sanding mill 1.0 and use it instead of the barrel trimmers. I have had 3 barrel trimmers (two were carbide) and gave them away. The sanding mill or off set sanding is the way to go. Some people even make their own.
 
I too do not use them any more but when I was I noticed that some cutters were not flat across and they did not cut a straight line across the blank. Tough to describe.
 
I only use barrel trimmers. May I say…. Don't try to use one on a blank that has been turned. It tears it apart.
 
WriteON said:
I only use barrel trimmers. May I say…. Don't try to use one on a blank that has been turned. It tears it apart.
Click to expand...

That is interesting .... new input, . . and it is very interesting.

I wonder if using the barrel trimmer on an already-rounded blank is related to the "45-degree" distortion of the outer fibers at the end.
This could give rise to an edge effect on the rounded blank's curved surface where the fibers are not fully supported on all sides.
The fibers at that outer curved surface could get distorted, or "torn", as you say ... without as many neigboring fibers for support.

For me, I like to trim the blank to length AFTER the blank has been rounded to a diameter of about 3/4" .
I feel that I get the blank to the correct length more accurately in this way.
Bear in mind that the "recommended" length for the blank is often never specified ..... the major exception being the PSI instruction sheets which, themselves, often specify the length only approximately to, for example, the nearest 1/32" and often not as value to 3 decimal places.
Of course, one should always MEASURE the tube length before gluing it in, and then you would know.
I don't like taking somebody else's word for it, especially when the instructions were written, in some cases, 10 or so years ago.

IF you do the barrel trimming with a square-cross-section blank, you may end up with a circular cavity at each end of the blank.
And it is then the distance between the bottoms of the two cavities which is the actual blank length.
It is rather hard to measure that distance in order to compare with the desired length.
You are going solely on that being the actual desired length of the brass tube, but you may have taken a few thou off the brass in the process (which you cannot visually track because of the cavities).
The result may be a somewhat shortened blank, resulting in the refill (for a BP or RB) protruding more than you would like.
I like to be able to put the trimmed blank between my caliper jaws so that I can measure the length accurately and adjust if desired.

The saving grace could be that the 3/4" ( or so ) initial rounding that I do is considerably larger than the final diameter so the 45-degree effect does not occur in the region where it would cause an undesirable final appearance.
 
But ..... I think we are getting away from the issue raised in the OP.

The OP says .... "After I turn the pieces to shape, I notice on the ends of the pieces that the grain of the wood isn't cut cleanly, but rather is bent over at like a 45 degree angle "

So his blanks are already rounded to the correct size, it would seem, before the barrel trimming .
( This observation by me may require further clarification by the OP ).
Perhaps that is the key to the OP's problem.

If you round first, then leave the end diameter LARGER than the desired diameter and go down to the final size AFTER barrel trimming.

Would that solve the problem that is the subject of the OP ? . Worth a try, I would think.

@BTS ... If you do try this altered method, please let us know the outcome on the "45-degree problem" at your barrel ends.
 
Angle. Maybe the wood has moisture. Wood is soft and twisted. However as stated try a new trimmer.
 
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KISS; USE A ROUND NOSE SCRAPER AND high speed with the tool rest set above the center. Ten years and the carbide cutters are in a drawer somewhere in the shop. P
 
I would go with a dull mill. I only use pen mills myself, but they must be sharp. There are some info on sharpening these things with a diamond card. Or you could see if any machine shop around might do it for you. I can offer, but not very cost effective with shipping both ways, unless you have more than one.
 
Looks like the end grain just does not like the angle of attack of the pen mill as mentioned above.

I stopped using the pen mills, for many of the reason stated, also issues with Polyester resin. @rherrell sanding jig for squaring just works every time, with any blank. https://www.penturners.org/threads/custom-made-penturning-tools-accessories.92501/

You can also turn round and still use the sanding jig. I would not turn all the way to exact though.

Good luck.
 
I notice a couple mentions of using a skew or scraper to trim the ends of the blanks... but, unless I'm misreading/misinterpreting/missomethinging, doesn't that just square the end of the blank relative to the exterior of the blank (with added uncertainty based on how straight it's being held in whatever type of chuck is used), rather than squaring it to the tube?

The only exception I can see (aside from counting on a perfectly concentrically drilled blank) is in the case of a pin chuck or something like the "grabber" closed-end mandrels.

What am I missing here? I'd love to ditch the barrel trimmers, but have yet to pick up one of Rick's jigs, so I'm always curious about other alternatives.
 
Thank you for everyone's reply! Much appreciated! I have a lot of leads to follow up on now.

To clarify a few things --

The blank shown in the photo is a black-line spalted maple. It does look like a crack in the blank, but it isnt. This maple is pretty soft, but I have had this problem with everything from maple to walnut, to tropical hardwoods. It is a common occurrence across many species for me.

I start with the square pen blank cut to length for the brass tubes being used. I drill the blanks, glue the tubes in place, then square the ends with the barrel trimmer. After that, I place both on the mandrel with the bushings (both the upper and lower blank parts for the pen), then turn them round / to shape which is the stage the blanks are in the original picture.

Yes, I have a sleeve on the barrel trimmer to match the diameter of the tube, so there isnt any slop there.

The trimmer feels sharp to the touch, but I guess if the angle is wrong on the faces, I can see that possibly causing an issue... I don't know if they are correct or not...🤷‍♂️

Barrel trimming speed -- That is very likely a contributing factor here just thinking about it. If I should really be running this at up to 1000 RPM as Magpens mentions, then the 300-400 RPM I have been using (it is about what I use to drill the blanks out as well) is probably very inadequate, and part of the problem.

I havnt tried to square them by hand with a skew or round nose scraper. I should give that a try... I don't, but should, trust my ability to trim them square by hand. I have thought about sanding them, but currently I don't have a set-up to do that.

I will try some of these suggestions and let you all know what happens.

Thanks again!
 
BTS said:
Barrel trimming speed -- That is very likely a contributing factor here just thinking about it. If I should really be running this at up to 1000 RPM as Magpens mentions, then the 300-400 RPM I have been using (it is about what I use to drill the blanks out as well) is probably very inadequate, and part of the problem.
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Not to put words in someone else's mouth (err... keys under someone else's fingers?), but I think Mal was only suggesting that speed with regard to using a skew. Personally I usually run a trimmer around 300rpm (although I do my trimming on my drill press rather than on the lathe, partially because it gives me a lower speed) - I find that higher speeds seem to just burnish the ends rather than cutting, and dull the trimmer faster.
 
@Bats

Bats said:
I notice a couple mentions of using a skew or scraper to trim the ends of the blanks... but, unless I'm misreading/misinterpreting/missomethinging, doesn't that just square the end of the blank relative to the exterior of the blank (with added uncertainty based on how straight it's being held in whatever type of chuck is used), rather than squaring it to the tube?

The only exception I can see (aside from counting on a perfectly concentrically drilled blank) is in the case of a pin chuck or something like the "grabber" closed-end mandrels.

What am I missing here? I'd love to ditch the barrel trimmers, but have yet to pick up one of Rick's jigs, so I'm always curious about other alternatives.
Click to expand...

It might be me that's missing something ..... Let me try to add something ..... with regard to "perfect concentricity" of the drilling .....
That "perfect" concentricity is certainly a desirable objective, and ... I believe ... can be achieved ... preferably before trimming to length.
You have to be very careful with every step below. . Read and understand all before starting.

1) Start with a square-cross-section blank cut to desired length + 3/8". . Should have ends QUITE square to axis ... strive for this.
2) Mark dimples at centers of both ends. . Mount on lathe between centers ... conical center tips go into the dimples.
3) Round this blank as accurately as possible along its length. . Remove the conical center from the headstock chuck.
4) Mount this "dowel" in headstock chuck accurately aligned with lathe axis. . A help in doing this is to use the already mounted tailstock conical center in the dimple at that end. . That should give you pretty accurate alignment to the lathe axis. . Tighten headstock chuck at this time.
5) Remove the tailstock cone and replace with your tailstock drill chuck holding a drill bit which is about 2/3 the size of the hole you need
6) Drill. . You should advance the drill at a fairly slow rate until it is halfway through the length of the dowel.
7) Drill again with the drill size increased to the full size you need.
8) Back off the drill. . Remove the drill chuck. . Restore the conical center in the tailstock.
9) Flip the dowel around. . Realign to lathe axis with help of conical center. . Tighten headstock chuck more. . Install tailstock drill chuck.
10) Drill first with the smaller size drill. . Change to larger, correct size drill. . Drill again.

At this time, you should have a drilled dowel with axial hole very accurately aligned to lathe axis .... hole concentric with dowel outer surface.
If this is not the case, a likely cause is that your dowel ends were not "sufficiently square" to the dowel axis; this threw off the drilling.

At this time you can glue in the tube .... center it in the dowel. . The next step is trimming to length, taking a little off both ends to JUST get to the end of the brass tube. . You MUST ensure that your dowel is accurately aligned to the lathe axis, as per my above methods, at each stage.
Use the tailstock conical center to align dowel to lathe axis every time you switch the dowel around.

My suggestion of using the skew chisel should work just fine. . You can actually use any method of trimming. . Be VERY careful. . Go SLOW.

Send me a Private Message if you need clarification or if you run into any trouble ... a pic(s) of your setup could be helpful.
 
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It looks, to me, that the trimmer is being pressed too hard and chamfering the edge. The dark line is created by heat, just like when you use a wire to burn the wood
 
I think, getting back to the original question, better advice could be given if you could show us a picture of a blank you have trimmed, but not turned at all. I can't fathom how a barrel trimmer could cause the rounded over edge after you've turned it down.
 
One other question, not really pertaining to your original question, just curious. In you picture, at the top, do you have a spacer between your bushing and live center? Or is your bushing on backwards?
 
Look, I am a beginner at pen turning. I use a barrel trimmer. It's just a plain tool steel (well, that's what they call it) but there are "tool steels" and real tool steels. Mine is somewhere in the middle. I find I need to touch up the cutting edges with a fine flat file fairly often to get the thing to cut without me lifting myself off the floor pushing down on the drill. It only takes a minute or two to just give the 6 teeth a quick rub with the file and you are back in business. Sharp is good, scary sharp is better.
 
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