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Comes down to accurately boring a long hole with a Criterion DBL-202B on a manual machine.

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
Background:
I borrowed four linear bronze lined bearings from this wood boring machine.
The three long levers are removed and hanging in a paint booth for painting today.
The router is mounted on the vertical plate and there is xyz movement.
Made with a drill press, hack saw, hand taps, and files. Made by my brother.

DSC_1485.JPGDSC_1486.JPG

My intent is to make linear bearings with UHMW inserts. Either it's going to be four (2 to a side) or two (1 to a side).
This pile of stock are my intended victums.

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1. The question is can a 4.5 inch long hole with 1.25 inch diameter be too much for the Criterion?
My experience with the Criterion is that when I tweak the adjustment knob at the end of a hole the thing takes out more stock than it should have.
Another thing is the recess of the bronze bushing in pic 2. It is 1/4 inch on both sides.

2. There is no locking ring so I ask why did they make the bushing 1/2 inch shorter?
3. What is a accurate way to get a 4.5 inch long slab of UHMW on a lathe. Using the center into a round of plastic does not inspire confidence.
I was thinking of making a cap of hard material for the end so that the center point would not deform the plastic.

Can't see paying money like this unless I had a bakery and needed something immediately before the bread was done.

 
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Hard to imagine that any boring head would have a problem boring a hole to size in UHMW. More important I think to have your spindle trammed very well and a proper cutting edge on the boring bar, whether insert or HSS ground tool bit. The part clamping will also come into play, as in don't clamp half the part in vise jaws and leave the other half in unclamped free-air condition.
 
Right now I have a Kurt with jaw height of 1 5/8 inches.
What do you think of building a fixture to mount the aluminum block on a lathe chuck and bore horizontal?
 
Since the linear bearings ID to OD concentricity is going to be critical, bore your holes first. Then make up a between centers mandrel that fits your bore size. Use that to turn the OD. How you clamp the linear bearing to the mandrel has multiple ways to do it. Even a hose clamp might be enough to provide a non slip drive while the OD is turned. A collar on the one end of that mandrel, threaded other end and a nut would also be enough to drive it as long as you don't over tighten and start to deform the UHMW.
 
My experience with the Criterion is that when I tweak the adjustment knob at the end of a hole the thing takes out more stock than it should have.
So everything is elastic, and deflects. Small DOC passes can deflect a significant fraction of the DOC, especially on materials like plastics and when cutters are less than perfectly sharp. When you dial in a small change, you may be shifting from "mostly rubbing" to "mostly cutting", which is one reason a tweak can take out more than you expect.

You should also check that the cutting edge of the boring bar is in the plane of the centerline and the DOC offset. If it is offset from that plane, you can get screwy results, although cosine error usually makes it a shallower, rather than deeper, cut.

When tolerances are tight, I generally do some experimentation before I reach my final bore size. Make sure I've got very sharp cutters, take several spring passes at the same boring head setting, measure the actual bore size, dial in a bore size change of a specific DOC, take the cut, measure the actual bore, take several spring passes, measure the final bore. This way, if I want to use a finish pass of that specific DOC to end up with a target bore size, I know where I should be before the finish pass, and how much (if any) the spring passes will clean up.
 
Thanks neanderthal, you a smarter than you look.

https://humanorigins.si.edu/evidence/human-fossils/species/************-neanderthalensis

The real question is this:
Is it an excuse to go a little beyond limits, assuming the insert bearing will be UHMW and will conform to machining screw-ups in the aluminum bored hole?
 
So everything is elastic, and deflects. Small DOC passes can deflect a significant fraction of the DOC, especially on materials like plastics and when cutters are less than perfectly sharp. When you dial in a small change, you may be shifting from "mostly rubbing" to "mostly cutting", which is one reason a tweak can take out more than you expect.

You should also check that the cutting edge of the boring bar is in the plane of the centerline and the DOC offset. If it is offset from that plane, you can get screwy results, although cosine error usually makes it a shallower, rather than deeper, cut.

When tolerances are tight, I generally do some experimentation before I reach my final bore size. Make sure I've got very sharp cutters, take several spring passes at the same boring head setting, measure the actual bore size, dial in a bore size change of a specific DOC, take the cut, measure the actual bore, take several spring passes, measure the final bore. This way, if I want to use a finish pass of that specific DOC to end up with a target bore size, I know where I should be before the finish pass, and how much (if any) the spring passes will clean up.
F. A. (if you know what I mean. I forget or am to cheap to sacrifice a new cutter for something I'm currently using.)

I am having to go study a bit on what you are saying here.
 
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I preferred HSS as it was easier to hone to a keen edge. The goal was to take off an almost transparent ribbon of material when approaching dimension. If it didn’t seem as sharp as it could be it was time to stop and hone again.
 
I looked and my longest bar is going to go only 3 1/8.
Hitting from both sides might work but there will be a discontinuity in the center, :nono:
 
Hard to imagine that any boring head would have a problem boring a hole to size in UHMW. More important I think to have your spindle trammed very well and a proper cutting edge on the boring bar, whether insert or HSS ground tool bit. The part clamping will also come into play, as in don't clamp half the part in vise jaws and leave the other half in unclamped free-air condition.
The hole is going to be in aluminum with a UHMW insert inside the hole.

The insert has a hole too. OD = 1.25, ID = .750. This is lathe work.

2LFL7_AS01.jpg
 
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What do you have for a lathe? If there's a tee slotted cross slide or any other method of fixturing work to it, then a between centers boring bar for the aluminum bores. It would be a job where having a lathe milling attachment comes in handy and why I have one even though I also have a BP clone.
 
When close boring I put a tenth indicator on the boring head slide so I can see exactly how much it moved and if it shifted when nipping up the lock. I’ll do the same thing on a lathe if I need too..
1. The question is can a 4.5 inch long hole with 1.25 inch diameter be too much for the Criterion?
My experience with the Criterion is that when I tweak the adjustment knob at the end of a hole the thing takes out more stock than it should have.
 
Do you really need a full length bushing?
Maybe use two bushing less than half length and then use the lathe to bore. then press in from each side. This way you can bore inside and outside in one operation for concentricity.
On MD nylon I used about .010 for finish cuts. The strings are thin enought they don't interfere. The cutting edge needs to stick out from the bar or the strings winding up will rub. A lot of boring bars don't have much clearance there.
So HSS in a slotted bar will work better. Plus sharp Hss has less tool pressure than carbide.
Dave
 
What do you have for a lathe? If there's a tee slotted cross slide or any other method of fixturing work to it, then a between centers boring bar for the aluminum bores. It would be a job where having a lathe milling attachment comes in handy and why I have one even though I also have a BP clone.
A Hardinge.
Are you suggesting that the work mounts to where a tool holder mounts and stick a boring bar into collet?
Then just move the cross slide into the boring bar. Never thought of that.

I'm thinking about using a wood lathe flange and a scrap aluminum piece mounted to the flange. Turn true and mount piece to bore.
It can be setup for production.
 
As has been mentioned - There are good reasons not to use a full length bored bushing.
It will be possible to exert better control over the ends of the bushing (where the wear will also be greatest) if the center is relieved. IOW you can tighten each end more yet still get good sliding motion, and the bushing assembly with have less tendency to cock or slew due to bellmouth, or differential forces that cause a somewhat compliant parallel bore to behave as though it were bellmouthed. So once you get a good bore in the aluminum, your bushing stack could be 3 pieces, of which only the 2 outer ends need be perfect on-size bores. The middle being slightly relieved on the ID.

UHMW is easy to machine, but difficult to maintain geometry. Cut all the features on ID & OD and verify, then cut it off and don't count on tweaking it much in place. It can be honed, but becomes a nuisance.

With that size lathe, mounting the work on the carriage, and the bar between centers, using the lathe as a horizontal boring mill, is probably the most reliable method. OTOH with a 3/4" or larger dia bar, it is not difficult to bore a hole like that on a mill, but hitting the same diameter at both ends might be, depending on the quill condition.

Then again, you can bore both ends for a shorter bushing, and forego the relieved bushing space in the middle.

smt

Edited: I do see your problem boring on the mill with that head, nice though it is - apparently it will only take 1/2" shank bars? Should be at least 3/4" to go 4"+ in Al. 1" might be better.
 
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Can't see paying money like this unless I had a bakery and needed something immediately before the bread was done

There are better, more rigid systems than the original Thomson round rod/ ballbushing version.

I understand that you are refurbing a legacy system that is complete, presumably once worked well, and may have other significance to you.
But don't consider the Thomson stuff as either ideal, or as some sort of benchmark for price. It's not used on machining centers, for instance. :)


No idea if this one is even close in size or travel for an app like yours, just a very quick grab of what is out there. Cheap.
You may have to work at dust shielding, though some have great provision for that, too.



And there are Thomson style, for non-Thomson prices.

 
Yeah Rons, that's what I meant, but I know zero about Hardinge lathes and just how easy mounting work to the cross slide would be. Without a lathe milling attachment, it gets a bit more complex blocking your parts up to the correct elevation to match your spindle center line. And with the way between centers boring bars work, you have to remove it for any hole size measurements. So running it between actual centers instead of one end in a collet is the most accurate and repeatable. For larger and longer bores and without more specialized machine tools, those between centers boring bars are about the next best method.
 
Yeah Rons, that's what I meant, but I know zero about Hardinge lathes and just how easy mounting work to the cross slide would be. Without a lathe milling attachment, it gets a bit more complex blocking your parts up to the correct elevation to match your spindle center line. And with the way between centers boring bars work, you have to remove it for any hole size measurements. So running it between actual centers instead of one end in a collet is the most accurate and repeatable. For larger and longer bores and without more specialized machine tools, those between centers boring bars are about the next best method.
The Hardy cross slide is not as rigid as I would like. I've seen it flex.
I'm working on another idea with a face plate.
 
imho its not going to work like you are planning. get some round stock for the lathe.

1) be sure to experiment with smaller pieces. let them sit overnight and remeasure. plastics have a kind of memory. i used to think the change in size was related to moisture absorbtion, but now im sure its not the only factor.

2) no way you get an consistent diameter that long. the part will distort due to heat.

3) dont clamp on the area being machined.

4) dont use any oils (best cooling would be by air).

5) rake >20°

edit:
6) in industrial practice the material is carefully annealed for best results, probably dependent on the brand in question.

7) glas transition temp can be as low as 100°c.
 
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