Re-boring Keyed Drive Hub - Ideas?

CalgaryPT

CalgaryPT

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I managed to source what I thought were the right size drive hubs for a project. The bore was supposed to be 17mm to accommodate the motor shafts which are just under 17mm. Sadly, when they arrived from the USA the internal bores are slightly too small at 16.59 and 16.47mm respectively. The shafts are both 16.97mm. In other words, even if they were intended to be an interference fit (which they are not), they would be too tight. In fact I can't even get the shaft on.

I'm fighting with the USA supplier but thought I'd ask for a backup plan in case they don't come through. Because it is a keyed shaft I'd need a spiral fluted chucking reamer to work the keyway. The hub depth is 2.3". I don't have any spirals, or any straight fluted 17mm reamers (which wouldn't work). I could take it to a shop, which I may do. I'm still looking for a affordable spiral online.

If the company does send me new hubs, the duty will be another 48 bucks. So I'm looking for cheaper solutions. Are there any lathe tricks for re-boring a keyed hole? Can it be done? The material is A36 I'm pretty sure.

What about a 17mm drill bit? Would the 118 degree point be sufficient to rebore these? That seems like the cheapest solution if it would work.

Any ideas??

hub2.jpg
 
ducdon

ducdon

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I would be more inclined to a 17mm end mill. I think a drill bit would just snag on the key way! OR. Cut down some key stock till its just flush with the bore ID. Red Loctite it into the key way. Then bore with a boring bar. When done heat it to release the Loctite and knock out the key? I have never done either of these, just ideas, but I do think you have to get the key way out of the equation till the hole is sized. Good Luck.
 
K

kylemp

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CalgaryPT said:
I managed to source what I thought were the right size drive hubs for a project. The bore was supposed to be 17mm to accommodate the motor shafts which are just under 17mm. Sadly, when they arrived from the USA the internal bores are slightly too small at 16.59 and 16.47mm respectively. The shafts are both 16.97mm. In other words, even if they were intended to be an interference fit (which they are not), they would be too tight. In fact I can't even get the shaft on.

I'm fighting with the USA supplier but thought I'd ask for a backup plan in case they don't come through. Because it is a keyed shaft I'd need a spiral fluted chucking reamer to work the keyway. The hub depth is 2.3". I don't have any spirals, or any straight fluted 17mm reamers (which wouldn't work). I could take it to a shop, which I may do. I'm still looking for a affordable spiral online.

If the company does send me new hubs, the duty will be another 48 bucks. So I'm looking for cheaper solutions. Are there any lathe tricks for re-boring a keyed hole? Can it be done? The material is A36 I'm pretty sure.

What about a 17mm drill bit? Would the 118 degree point be sufficient to rebore these? That seems like the cheapest solution if it would work.

Any ideas??

View attachment 5648
Click to expand...

I don't have a reamer in that size but I do have a lathe. Boring in the lathe is the best way to go, the keyway shouldn't be a big problem.. As long as you don't then need a deeper keyway because of the diameter change (not like a reamer would change that). A drill would not be accurate though for running on a shaft in all likelihood. If you have hand adjustable reamers maybe you could put something in to bridge the keyway, but I don't think it would work very well.
If you don't get the supplier to eat the cost and want to proceed give me a shout and I'd be happy to help you out. Depending on what you're doing cutting the hubs off and making new ones, welding them in and finish boring may be even better.
 
CalgaryPT

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I have a lathe that can handle this easily but you can't bore a keyed hub as far as I know--that's why a spiral chucking reamer is recommended I think. A boring bar just catches the keyway. On a spiral reamer the flutes aren't perpendicular so they can bore a keyed hub easily. But they are SO expensive.

Never thought about the keyed stock and Loctite solution. That's pretty bloody clever. I'll have to think about this.

Just heard from the manufacturer a few secs ago—they are going to replace the hubs. I'm almost disappointed as I wanted to try to fix these. Plus, they want the old ones back so I don't get to play. I asked them to throw a telescoping gauge and calliper on them before they ship as I am paying duty a second time.

I need to learn how to broach keyways myself again. I hate being dependent on manufacturers.

Thanks all for the offers and advice.
 
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Janger

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Sounds like you've got it solved - but what about turning down the shafts instead?
 
K

kylemp

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I've never had any issue boring out with a keyway in the way, although it takes more time and is more likely to chatter, it would be the same as any interrupted cut. You couldn't reasonably drill it because of the keyway but single point cutting wouldn't be an issue. Based on your parts, I'd be buying off the shelf hubs (or making them if you have the tools and time), have them torched out, or milled depending on what you need for accuracy, make them a close fit to the bore on the mounting flange or press fit, weld them and face them true. I'll give you a hub with a keyway if you want to try boring one out, it's nothing too difficult unless you have small boring bars. Good practice.
 
CalgaryPT

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Janger said:
Sounds like you've got it solved - but what about turning down the shafts instead?
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The motors are worth almost $500 each so I'm reluctant. I guess we'll see when the new hubs arrive. I think the company is a tad ticked at me, or maybe just at themselves. I know they contract out the parts and make them in batches; I don't think they QC'd the shipment as they didn't believe me until I sent a video. Even the pics I sent them with generic digital callipers inside wouldn't suffice. (They told me I was measuring burr on internal set screws). So together with the vid of them not fitting I included pics with a telescoping gauge and a Mitutoyo. Based on the last email I got from them where they caved, I think they learned a lesson too. And I suspect their machine shop got a call from them. If they manually turned these maybe some of the others are OK. If they CNC'd them I'm sure someone is on the bad list.

I wish the shafts were imperial; there are so many more options available to buy drive hubs and cut a circle out to make the wheel plate.

Thanks John.
 
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CalgaryPT

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kylemp said:
I've never had any issue boring out with a keyway in the way, although it takes more time and is more likely to chatter, it would be the same as any interrupted cut. You couldn't reasonably drill it because of the keyway but single point cutting wouldn't be an issue. Based on your parts, I'd be buying off the shelf hubs (or making them if you have the tools and time), have them torched out, or milled depending on what you need for accuracy, make them a close fit to the bore on the mounting flange or press fit, weld them and face them true. I'll give you a hub with a keyway if you want to try boring one out, it's nothing too difficult unless you have small boring bars. Good practice.
Click to expand...

I've never tried it, but you have me interested. I just assuming it would chatter to heck. I do have some old imperial hubs from PA in a box in the shop. I'll see if I can find them. I don't think they are hardened. I do have boring bars that should do the trick. Any other tips?
 
Tom Kitta

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"If the company does send me new hubs, the duty will be another 48 bucks." OMG how much are the hubs? That duty implies almost same as the motors - $1000? If its duty plus border fees you need to get yourself BorderBee service or similar. It is like $15 + some small stuff + GST for items under I think $1000.

I check whatever I have spiral reamer in the 17mm size - but that is somewhat hard to find in that size - I can look for 16.96 to say 17.01mm.

I think a drill bit in say the 16.9mm range would work as well as long as you don't want a perfect fit. You can drill and then you can use some emery cloth to make it smoother. I would not use 17mm drill unless you want some slop in there or use loctite or some other solution - you have 0.1mm of extra dimension.

For interference fit you are usually looking at very fine amounts - I always struggle on a lathe or mill to get the interference fit just right. With shafts at 16.97 I venture they want the hubs at around 17. Interference would be 16.96 or 16.95 maybe 16.94 would work as well - anything more and you would need to heat up the hub red hot and put it on the shaft to cool down and shrink.
 
CalgaryPT

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Tom Kitta said:
OMG how much are the hubs? That duty implies almost same as the motors - $1000? If its duty plus border fees you need to get yourself BorderBee service or similar. It is like $15 + some small stuff + GST for items under I think $1000.
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Hubs were $47 USD, so say $60 CND. Duty and all the other clearance charges came to about $24 each. Not that unusal. Everyone says get a PO Box in Sweetgrass, but every time I crunch the numbers it doesn't make sense. Plus, I'd need a passport, which I don't want to buy because I don't travel...especially to the USA.
 
CalgaryPT

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I will John. Actually it is two in one. I have a friend who needs to do inspections inside an underground structure so he wants one. But I always wanted a RC lawn motor with differential steering due to the low hanging trees in our backyard and my bad back. So I am building the base to accommodate both—but I will likely end up with it as a lawn mower most of the time. I am basing it on this model:


For the past three months I have been testing motors, motor controllers, Buck convertors, LAC boards, RC transmitters, Arduino fail safes, etc. I finally have all of that stuff working and have the motors and tires. I just need the mower itself and the batteries (motors are wheelchair 24V - 300 watt beasts). But I am still deciding on gas or electric for the mower (leaning towards electric). I likely won't buy the mower until late fall or next spring when they go on sale if I opt for the electric (battery) option.

The fun part is approaching: the metal work on the frame to accommodate either the mower or the test equipment that needs to fit in it. In the above video I have bought the exact same motors, tires and am using its basic design, but will build a drop-in module to replace the mower and accommodate the test equipment he needs. I also will include a 150 lbs. linear actuator to raise and lower stuff for his purposes, so I wanted to see if I could use the same actuator setup to raise and lower the mower deck height for my purposes (geeky I know). Sadly, I don't think the geometry on this will work for me, but I'm still prototyping with cardboard.

Either way it's tons of fun. A crane hoist will help me lift the unit to service it in my shop, as its estimated weight with batteries could be as much as 300 lbs if I use a gas mower. Instead I'm liking the brushless Kobalt mower that they use in the vid, but the 5AH batteries are hard to find as replacements—which I know I will need after a few years. This is the downside to battery powered mowers: lifecycle replacement cost.

It's a long term project, but I will post pics as I get deeper. I'm a little stalled now awaiting the mower decision and his module specs, so thought I'd build the crane while I wait. Both the crane hoist frame and the smaller 800 lbs electric hoist go on sale at PA frequently, so I'm watching it like a hawk.
 
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Johnwa

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That’s an interesting project, sounds like a lot of fun.
I had to google Kobalt mower. It looks like their battery pack has the same rating as hoverboard batteries(36V 4.4 Ah). Charged they are about 42V. The best price I’ve found is on amazon.com, $40 US free shipping. The one I got shipped from China but did have Samsung batteries (I opened it up to check)
 
CalgaryPT

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Johnwa said:
That’s an interesting project, sounds like a lot of fun.
I had to google Kobalt mower. It looks like their battery pack has the same rating as hoverboard batteries(36V 4.4 Ah). Charged they are about 42V. The best price I’ve found is on amazon.com, $40 US free shipping. The one I got shipped from China but did have Samsung batteries (I opened it up to check)
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Thanks. You can buy the mower with the 5AH battery but the lawn mower forums show it as almost impossible to replace with OEM. My experience with after market replacements have all been failures. Apparently 90% of them are fakes, and many tested have less than 30% of the rated capacity. I'm hopeful this is improving over time.

This is why I am still wavering on mower choice. Gas ones are cheap, but I want remote start, which is impossible to find w/o propelled drive...which is wasted weight that I need to consider. Also, they are more complicated to stop the blade rotation w/o shutting down the engine.

But you are correct. It is a fun project. I never realized the science that went into mower decks, and how the air flow creates a vacuum to suck the grass up straight prior to cutting. I saw one fellow build his own deck and attach a 12V motor to the blades to circumvent the battery lifecycle issue. He used a Buck convertor off the 24V source for the mower. But w/o the right RPM and deck design, there's no vacuum.

I love learning stuff like this. I will do more battery research. Another backup plan is to make a more generic battery holder for the mower power so I can use different brands. But supposedly the higher end mowers/packs have proprietary chips in them now like ink jet cartridges to prevent non-OEM replacements. Can you believe this?
 
Tom Kitta

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CalgaryPT

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Tom Kitta said:
Why don't you make it full on custom by building a battery out of standard Li-Ion batteries https://www.batteryspace.com/hi-pow...2-24wh---ncr18650b-0-93---un-38-3-passed.aspx

I guess charge controller would be an issue and custom management.

People seem to make their own so it cannot be that hard - https://www.instructables.com/id/DIY-Professional-18650-Battery-Pack/

The plus is that you are not tied to one battery type. Minus is extra work and I think custom pack is more expensive.
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You're right. And I'm looking into a variation of that. Charge control isn't that difficult but OEM packs often have safety features that aren't practical on individual cells (as I think early Teslas discovered). Lots of guys have done the same but at a certain point it isn't cost effective, assuming you can find the replacement OEM pack. So it's a bit of a gamble as well: will the OEMs be available in a couple of years?

Another strategy is to make the frame adjustable to accommodate another mower brand. That way in the future you can replace the whole unit if necessary.

All fun to think about...
 
Johnwa

Johnwa

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A BMS for 36V ebike batteries is about $20 depending upon the maximum current that has to be supplied. It controls the charge and has built in battery protection. They aren’t true balance chargers but are still supposed to balance the batteries.

I happen to have a partially built spot welder for building battery packs. No idea when it will be finished
 
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