Slitting a Brass Bushing

[Tecnico]

Just a quick one this evening, I’m looking for some advice from the depth of experience that hangs out in these parts. I’m working on a project (more later) and I have a bushing I want to slot and I could use the voice of experience before I get too far into the job. The part is:

Brass

Outside Dia: ~1.25”

Length: ~1.425”

Bore~0.5”

I want to cut a .125 wide slit along the length that breaks into the 0.5” bore. A 0.125” thick key fits in the slot and I want the fit to be “tight” without appreciable slop. The key will be held by fasteners which basically clamp the slot onto the key. Essentially, I’m making a bushing with an internal key.

I have two “slitting” tools on mandrels, one .125 thick (4” dia), one .117" thick even though it claims to be .125 (2.5 dia), my question is, can I depend on the .125 tool to cut close enough to .125 that the .125 key will be a “tight” fit or can I expect it to cut an appreciable amount wider in which case the .117" cutter comes to mind for a two (or more) pass process to sneak up on the .125 dimension?

The tools look like good quality pieces, they’re SKF and seem sharp even though they’re probably years old although the mandrels may not be high precision. I haven’t tried them, they came with the mill.

Also, should this be done in several passes (depth of cut) or right through in one pass?

What am I getting into here? Advice?

Thanks,

D

 

[PeterT]

You might be better off gripping the bushing in the machine vise by the ends & milling the slot with undersize end mill. First through, then finishing pass on either side & get exactly the fit you want.
**Hmmm I just thought about this some more. Your cut depth will ne 0.375" That might be pushing a say 3/32" dia end mill. Might want to experiment on scrap to be sure

Saws are kind of slower going. If you do a series of progressive depth cuts you might have some minor cosmetic ridges. If you do it all in one pass you might have to baby it a bit & there is always the potential of some drift depending on diameter & spring effect (gap opening) although brass should be pretty stable. I'm not sure if saw kerfs are ground to the thou vs. nominal dimension, might depend on quality.

 

[DPittman]

Also, should this be done in several passes (depth of cut) or right through in one pass?

I've read in more than one place that a saw blade/slitting saw should be used at full depth in one pass. I haven't done alot of slitting saw stuff but I initially was doing it also in multiple passes until I read not to. It seemed to work well in one pass.

 

[eotrfish]

For what it’s worth YMMV

I’ve cut several slots in 360 brass and 642 bronze sleeves using a .053” slitting saw - full depth / one pass. All came out precisely .053”. I’ve also cut several .032” slots which did not turn out well. The thin blade flexed - possibly due to uneven tooth wear. I think your .125 blade should be fine providing that teeth are in good shape.
I’ve found that the blade will produce a ringing sound if it deflects - otherwise you’ll only hear the teeth cutting.
Practice on a scrap piece
Good luck

 

[PeterT]

That's a good point. The thicker 0.125" blade should offer more rigidity.
Also (and here I always get confused) there are slitting/sawing blades & jeweler type 'saw blades'. I think slitter tooth count : diameter & profile are meant for this kind of work. Jeweler have many more teeth & different tooth profile. On certain blade thicknesses there is overlap sizes.

I actually only did brass & bronze once & seem to recall it was easier sailing vs. aluminum which is gummier & really does need cutting fluid lubrication. The deeper DOC all-in-one pass mode was just more challenging keeping an even but turtle slow feed pressure on. Any more & blade can Pringle chip. I tried different rpm's but it seemed to favor 'slow'. All this might be a function of depth & kerf width & material. I've never done steel yet.

I bought a new arbor & saws off AliExpress (metric) which I'm anxious to try. They are straight shank 16mm vs my R8 rig which I think is really intended for bigger cutters.

 

[PeterT]

Tom Lipton video. His sketch of chip evacuation provides a good visual.

 

[Former Member]

That's a good point. The thicker 0.125" blade should offer more rigidity.
Also (and here I always get confused) there are slitting/sawing blades & jeweler type 'saw blades'. I think slitter tooth count : diameter & profile are meant for this kind of work. Jeweler have many more teeth & different tooth profile. On certain blade thicknesses there is overlap sizes.

I actually only did brass & bronze once & seem to recall it was easier sailing vs. aluminum which is gummier & really does need cutting fluid lubrication. The deeper DOC all-in-one pass mode was just more challenging keeping an even but turtle slow feed pressure on. Any more & blade can Pringle chip. I tried different rpm's but it seemed to favor 'slow'. All this might be a function of depth & kerf width & material. I've never done steel yet.

I bought a new arbor & saws off AliExpress (metric) which I'm anxious to try. They are straight shank 16mm vs my R8 rig which I think is really intended for bigger cutters.

I work with Aluminium a lot, I must say I don't find it gummy unless:

1. Cutting teeth do not have enough clearance for scarf produced (more on this later).
2. Heat is not control.
3. Dull cutters

All of these actions produce heat which cause aluminium to smear or at worse friction weld. Scarf entrapment just adds fuel to the fire as it creates the perfect mix for welding.

 

[Susquatch]

A 0.125” thick key fits in the slot and I want the fit to be “tight” without appreciable slop. The key will be held by fasteners which basically clamp the slot onto the key. Essentially, I’m making a bushing with an internal key.

I repeat your question for a reason. Why worry so much about the exact slot width if you are going to "clamp the slot onto the key" anyway?

Instead I would rough drill the center hole first, then cut the slot (full depth in one pass with the smaller blade - go slow), then make the clamping arrangement and then insert and clamp a temporary key (one made just for use in the next fabrication step that is not as wide as the slot width so it does not affect ID or OD machining), then turn/bore the outside and inside diameters with the temporary key in place. This way you are guaranteed a perfect fit on the shaft and a perfect key clamp too.

If you want, you can also use the 1/8 blade instead. It all depends on how much you want to pretension the key clamping. Neither blade will affect the final assembly because of your order of operations.

 

[little ol' e]

That's a tuff call, either way. I would make the key to fit the final slot size if it were me.

 

[historicalarms]

I wouldnt cut the key slot to fit my key stock in one pass to get the tolerance of fit you require. There will be a little tension relief to the bushing when you cut through the body that may open the cut up bigger than your key stock...cut the slot twice to fit your key stock or cut slot smaller than key stock and then file fit for the tolerance you require.

 

[RobinHood]

Essentially, I’m making a bushing with an internal key.

So why would you slit the bushing right through to the outside? Just broach a keyway into the bore of the bushing? Brass is easily broached with HSS tooling that you can grind yourself. Start undersized in width and side step for the perfect fit to the key you have.

You don’t even need a broach/broach bushing; a single lip cutter will work perfectly fine. You can use it on either the lathe (moving the carriage) or the mill (moving the quill).

 

[Tecnico]

Thanks for the replies so far, lots of good input - keep it coming!

For context, I'm upgrading a drill press my father built more than 70 years ago, maybe as a school project. He was trained as a machinist which eventually led to teaching in vocational school. Unfortunately we lost him too soon for me to have learned much shop practice. He had a South Bend in the basement which my mother wisely(?) sold to keep small hands out of it........

The drill press uses a 1/2" diameter shaft sliding in the keyed bushing of the drive pulley on the quill shaft. Right now it has two sets of stepped belts for drive but I want to experiment with a DC treadmill motor to replace that drive train. The fundamental step is to replace the chuck/quill shaft driven pulley with a ribbed flat belt drive compatible with the treadmill motor. The current setup uses a bushing that looks like the image below but they're only available in 5/8" shaft size ($USA100!). I don't know how my father created the one he used but it is a single piece and brass. I don't want to separate it from the stepped pulley in order to keep an unmodified backward path. Just to highlight, the chuck/quill shaft slides in the pulley bushing as the quill is extended so the key must be fixed in the bushing. It's not a splined shaft like other configurations I have seen.

Some thoughts from your comments above:

@RobinHood What I'm trying to achieve would ideally look like this which appears to be a casting but is not available with a 1/2" ID:

Since I can't buy this part, instead of the outer key I would use fasteners in the end face of the bushing to mount it to the ribbed pulley. It only needs to carry torque.

You don’t even need a broach/broach bushing; a single lip cutter will work perfectly fine. You can use it on either the lathe (moving the carriage) or the mill (moving the quill).

If I could find a correct size bushing, that would work well for the outside key. It's a process I've done in the past.

Why worry so much about the exact slot width if you are going to "clamp the slot onto the key" anyway?

@Susquatch The answer is probably filtering out of the replies so far but basically I want to achieve the tight fit so I don't have to "come onto" the fasteners that clamp the key in place too hard to make up for an excessively wide slot (clearance). I'm not sure how much I can close the gap but I doubt it is much given the wall thickness. The advice of machining the ID after fitting the key is good (temporarily replacing the key with an equal thickness fixturing shim).

@little ol' e The advice to make the key fit the eventual slot is good as well.

@PeterT Good video, I learned some more things about blades!


At this point the one thing I have convinced myself of is that I will need to make a new arbor because the one I have now (came with the mill) has seen better days and gives a .005" wobble on the side face of a 4" diameter cutter, not a good starting point!

I'm interested in any other thoughts, even how I might approach this differently because I'm probably well set into confirmation bias on my approach!

Thanks!

D

 

[little ol' e]

I'm interested in any other thoughts, even how I might approach this differently because I'm probably well set into confirmation bias on my approach!

Thanks!

D

I have two “slitting” tools on mandrels, one .125 thick (4” dia), one .117" thick even though it claims to be .125 (2.5 dia), my question is, can I depend on the .125 tool to cut close enough to .125 that the .125 key will be a “tight” fit or can I expect it to cut an appreciable amount wider in which case the .117" cutter comes to mind for a two (or more) pass process to sneak up on the .125 dimension?

The tools look like good quality pieces, they’re SKF and seem sharp even though they’re probably years old although the mandrels may not be high precision. I haven’t tried them, they came with the mill.

I think you have a good approach, but I wouldn't go with the .117 with 2 passes, it will just chatter up an aweful noise on the second pass. If I were to tackle what your trying to do... If you have a rigid set-up, I would use the SKF .125 run it around 80-120 RPM and feed it slowly in 1 pass. Use an air gun to keep things cool and the chips out of the way for a nice clean cut.
Worse case scenario, you would need to make a new stepped key from the final size you get.
I would even consider using a 1/8 ball nose on the mill stepping it down, but not a 1/8 e'mill .

Whichever way you do it, I hope it works out well for you, which I'm sure it will...
Sorry to hear your Dad past away so soon, he will be over your shoulder helping you along the way with this... So no worries, you got this!

 

[Tecnico]

Whichever way you do it, I hope it works out well for you, which I'm sure it will...
Sorry to hear your Dad past away so soon, he will be over your shoulder helping you along the way with this... So no worries, you got this!

Thanks, I'll soak in all the good advice, process on it and it'll work out in the end.

It's kind of eerie, I've found that I developed some similar interests to my father even though he wasn't there to provide influence so maybe some of that does get passed on.

D

 

[DPittman]

Thanks, I'll soak in all the good advice, process on it and it'll work out in the end.

It's kind of eerie, I've found that I developed some similar interests to my father even though he wasn't there to provide influence so maybe some of that does get passed on.

D

It happens! Genetic imprint or something like that. I find myself doing things that my father did when I was a lad that annoyed me and now guess what I'm doing? Annoying my son with same or similar things. Apparently traits/manners/habits/etc can be passed on just with genes and not necessarily things we tend to think you had to be around the other person to pick up either.

 

[Susquatch]

It happens! Genetic imprint or something like that. I find myself doing things that my father did when I was a lad that annoyed me and now guess what I'm doing? Annoying my son with same or similar things. Apparently traits/manners/habits/etc can be passed on just with genes and not necessarily things we tend to think you had to be around the other person to pick up either.

I find this stuff fascinating. I never pass up an opportunity to read the latest research in this field.

I think we need to remember that most animals that are much less intelligent than humans have amazing abilities that are geneticly passed on without any learning whatsoever. I think our human egos tend to assume that our superior brains learn and control everything we do, but the reality might be much much more primitive.

 

[johnnielsen]

Some studies of identical twins separated at birth mention that these people often dress in the same way, grow beards etc identically and have similar interests in occupations and hobbies.

 

[Tecnico]

Time for an update.

Rolling all the advice together with everything else, I had a go at the slit and came out....successful! I'm quite pleased with the result, it turned out as I was aiming for.

I made a new arbor for the saw disc (4" @ .125 Nom., HSS), set the bushing up in the vise and had a go at it. Set up to 80 RPM, slow power feed and proceeded using WD-40 as a lubricant/coolant. After all the effort to make an as perfect as possible arbor with a tight fit on the saw etc. I was a bit surprised to hear the zing - zing - zing of an uneven blade. I suppose nothing is perfect especially with a used saw, not bad but not perfect.

Anyhow, here's how it turned out including the key:

And another view including the drive plate:

The key can be pushed into position by hand after a small amount of dressing of the slit surfaces although I actually milled it down to about .122", getting it flat in the process. The slot came out slightly undersize.

Next up, the multi-groove, flat belt sheave & bushing.

D

 

[little ol' e]

Nice Job ! Good to hear its working out so far...