New Tyres on my Puma 40

Power wheelchair board for REAL info!

POWERCHAIR MENU! www.wheelchairdriver.com/powerchair-stuff.htm

Re: New Tyres on my Puma 40

Postby woodygb » 04 Aug 2019, 00:15

An expert is a person who has made all the mistakes that can be made in a very narrow field.
Niels Bohr
User avatar
woodygb
 
Posts: 5677
Joined: 12 Mar 2011, 18:45
Location: Bedford UK

Re: New Tyres on my Puma 40

Postby Irving » 04 Aug 2019, 06:51

I would be somewhat surprised if the PN value was much of an issue... The 'spigot' section is 75mm OD, and the couplings from different brands seem to be about 47-50mm, so that gives about 12mm ~1/2" worth of 'meat' around the outside - even in aluminum that seems pretty stout...

Yes, I was being over-cautious. With the largest PN value of 120N/mm2 and a 47mm ID for the hub the strain is well below the limit for Ally. (I think I was reading the units of PN as kN/mm2 which would be a different story!)

Does it make any difference if the width of the hub is more or less than the width (length) of the coupling?

Given the above, probably not, though very thin sections will be prone to twisting and very wide ones might be difficult to centre the coupling under the hub (unless you use the flange type). I'd be looking at ~8-10mm min thickness as a gut feel.

Even though 3/4" is not quite = 19mm (0.75" = 19.05mm, 19mm = 0.74805" according to my digi-micrometer) should I assume that it is close enough to be able to use a metric fitting (I have seen some inch versions as well)

The various versions quote tolerances as typically h8 - h11 (shaft) and H8 - H11 (hole), which for 19mm means the max difference between shaft and fitting or fitting and hub is +/-23 -> 130um. On that basis I'd say it's close enough. What's the shaft measure at?
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 04 Aug 2019, 23:14

Since the web on the wheel is 8mm thick, I figure that I need to make the spigot at least that thick to look right, thicker is OK within reason, but why waste material if not needed... I was using the 16mm on the drawing that I posted to provide room for the cross bolt - if I get rid of the bolt, then I can go back down...

I am making the flange 8mm since that is the bolt size, and I've generally seen the rule of thumb that threaded length should be the same as the bolt diameter...

Gives me a minimum of 16mm.... In the couplings I've looked at so far, I have seen several with about that length of mating surface....

The shaft seems to be almost exactly 0.75" Diameter - and the Invacare part book calls out the key at 3/16" which is the standard size for a 3/4" shaft... There is some corrosion and assorted dings on the shaft, but it is pretty consistent... Just now I checked it again w/ my digital mike - locking the spindle, I could BARELY slide it over the shaft at 0.7500" and not at 0.7495"... If I do the clicker on the spindle it comes in around 0.7502 - 0.7503"

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 05 Aug 2019, 03:20

Another question Irving, and maybe BM or Woody -

I am seeing an 'Axial force' spec on some of the couplers I am looking at - which I assume is what it takes to slide the coupler back and forth on the shaft, or push the hub off the outside??? The units are KN, with a range from 33KN to 10.4 KN... The KN, or even the plain N isn't a unit where I have any sort of feel for what it means....

What is the max I should expect a chair to be able to exert? / minimum I should look for in the coupler.... Figure driving like BM.... :clap

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Burgerman » 05 Aug 2019, 03:28

I cant see any way to reliably measure that or even determine what a chair may apply. If it looks right it probably is. If you worry, add a spacer behind, and a nut and washer + spacer if needed on the outside edge. So it cant move.

But keyways and reversing loads do not work. I had to replace stock F55 wheels because of fretting. And subsequent wear. Parallel shafts are a bad idea. You need taper ones. With a key just in case. And steel preferably.

Threads. Ideally the thread in steel needs to be 1.25x the diameter. And in anything softer, more...
User avatar
Burgerman
Site Admin
 
Posts: 46370
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 05 Aug 2019, 04:06

Burgerman wrote:I cant see any way to reliably measure that or even determine what a chair may apply. If it looks right it probably is. If you worry, add a spacer behind, and a nut and washer + spacer if needed on the outside edge. So it cant move.

I don't really need a precise answer on the Axial load, just more or less of a 'ballpark' figure to say whether or not I really need to worry about it...

I'm thinking a full throttle 'bootlegger' turn, possibly sliding the chair sideways into a curb (and managing not to flip....) as the extreme case....

I did just try duck ducking for KN, to see if I could get a better understanding of it, which helped some, although I have a better feel for US values... A converter told me 10.4 kN ~ 2,338+ lbs of force, or a little over a ton, which feels like it "should" be enough, but I'm not sure I'm figuring it right...

But keyways and reversing loads do not work. I had to replace stock F55 wheels because of fretting. And subsequent wear. Parallel shafts are a bad idea. You need taper ones. With a key just in case. And steel preferably.

I totally agree about the badness of keyed shafts - which is why I'm going through all this. It would have been far easier just to do the same sort of keyed hub that Invacare used....


Threads. Ideally the thread in steel needs to be 1.25x the diameter. And in anything softer, more...

Hmm... I believe the 1xD that I'm thinking of came from the usual dimensions for nuts, although I just did some checks on random hardware out of my stash, and most actually seem less than 1xD... It doesn't seem critical in this case, as in my original idea, they would just be holding the wheel bolts in place while I put the nuts on the outside...

OTOH I've been thinking about possibly using putting Helicoils in the hub, and screwing the wheel down w/ Allen bolts instead - the couplers secure w/ Allens, so using the same thing on the wheel itself might look nicer... If I did that, I'd change the flange thickness to match the length of the Helicoil inserts....


ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Irving » 05 Aug 2019, 04:21

@goose: yes, axial force - along the axle - for these fittings is the force needed to budge them once torqued up. You won't get close to that by at least an order of magnitude on a wheelchair so no worries.

As to a 'feel'. The full weight of chair and rider is say 300kg. That's 3kN - you could hang 10 of them on one fitting and it wouldn't budge!
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby Irving » 05 Aug 2019, 05:18

The other issue is pull out force and shear strength of the bolts/studs.

Shear strength is easy, for our needs a grade 8 steel or stainless bolt bigger than M6 is more than adequate.

BMs rule of thumb of 1.25 x diameter for thread engagement works for steel bolt in steel thread (it's based on the nut stripping force being 80% of the bolt stripping force and the bolt failing before the thread does). If your hub is Ally not steel then you need to (theoretically) multiply by 3, but x 2 is often used.
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 06 Aug 2019, 04:08

I'm using M8 for the wheel bolts as that is the biggest that will go through the holes in the wheel... If I stick to my original plan, its certainly going to be strong enough as it would require pulling the bolt head through the plate....

If I switch to putting Allens into the hub, I figure that the Helicoil people should have a pretty good handle on how long their inserts need to be, especially since they are somewhat intended for use in aluminum... So if I make the bolt flange as thick as the insert length, it won't be going anywhere....

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Irving » 06 Aug 2019, 08:55

ex-Gooserider wrote:I'm using M8 for the wheel bolts as that is the biggest that will go through the holes in the wheel... If I stick to my original plan, its certainly going to be strong enough as it would require pulling the bolt head through the plate....

If I switch to putting Allens into the hub, I figure that the Helicoil people should have a pretty good handle on how long their inserts need to be, especially since they are somewhat intended for use in aluminum... So if I make the bolt flange as thick as the insert length, it won't be going anywhere....

ex-Gooserider

If using helicoils in ally their recommendation would be 1.5d = 12mm depth and min distance from outside of receiving hole (10mm) to edge of component of 0.375d = 3mm, using part M8 x 10 x 12.
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby Burgerman » 06 Aug 2019, 09:52

My advice if its thin. Use studs facing outwards. As used in a car.

M8
Easy to find.

Image

OR use countersunk steel allen bolt from the rear in the same way if it must be flush on the back face.
User avatar
Burgerman
Site Admin
 
Posts: 46370
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 13 Aug 2019, 05:32

I thought of studs, but bolts are even easier to find...

The advantage of doing Allens into the flange would mostly be cosmetic - the couplers all use Allens to tighten them, so it seems to me like it would look better to have matching Allens holding the wheels on rather than nuts...

Just for curiosity sake, I just dug out my two collections of Helicoil inserts (Neither is 'genuine Helicoil' but....) the M8 inserts in my '200 pc Assortment' are just about 11mm long, not counting the tab. This is close to what you suggested Irving... The ones in my kit (does M5, 6, 8, 10, & 12) are only about 8mm....

Side note Irving - You said earlier that you had found several links to stainless steel versions of these couplers - can you send me at least the brands? So far all I've found besides the one McMaster link that Woody sent is steel....

Thanks,
ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Irving » 13 Aug 2019, 11:08

@goose, an example:

http://www.ringfeder.com/en/internation ... ct/?p=9878

What I also found is most manufacturers do SS versions although the default is zinc-plated steel. For example US manufacturer Climax C193 series is zinc-plated but C193-S series is SS but it's not obvious from catalogue.
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 14 Aug 2019, 05:04

Thanks for the suggestions...

Looking up bolt strengths for M8 bolts, it seems even assuming the wimpiest grades, 4 bolts seems likely to be massively stronger than any load I could put on the wheel, so it seems like it wouldn't be a big concern to use the longer size Helicoils with Allen bolts....

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 24 Aug 2019, 02:11

Good news / bad news... Advice????

I have done a lot of research, and compiled a spreadsheet on all the companies making locking assemblies that I could find, with specs on their offerings for 3/4" - 19mm diameter shafts... :geek: serious eye strain....

There were two basic styles - cylinders that were the same diameter for the full length, and what I called "top-hat" where there was a larger flange for the screws that stuck out past the mating surface. The cylinder type supposedly could allow the hub to move back and forth while being tightened and the top hat wouldn't. In some cases the top-hat style had a slightly smaller OD on the mating surface.

The movement thing I don't see as a big issue, otherwise the difference is mostly cosmetic. I am pretty certain that I have enough room on the shaft to fit either style, and it seemed to me like the top-hat style might be better looking.

Some choices seemed much better than others if I tried to find parts that:
[*] Minimized the OD (leaving more meat in the hub)
[*] Had mating surface lengths that were fairly short (less material in hub needed)
[*] Had narrow rims if top-hat style.

I came up w/ one or two best options for each brand.

So far so good.... Now the bad news starts....

Knowing the chair will be used outdoors in New England winters with all the road crap, plus the year round rain and so on, my thought was that stainless would be a better choice than steel....

Figuring it might be better / cheaper to use a US manufacturer to stay in the US, and because it seemed to have one of the overall best choices, I reached out to Climax Metal Products, https://www.climaxmetal.com/. They had several that looked workable, and one that seemed ideal, the C-193-075....

The sales droid that replied to my request for quote, had a lot of bad news....

Yes, we do offer the C193E-075 in stainless steel, but we typically do not stock stainless locking devices on the shelf at our warehouse in Mentor, OH. They are manufactured at our factory in Italy and then shipped to our warehouse in about 5-7 weeks after we get an order.
(So much for US mfg.... banghead )

then:
[quoteI have attached a steel C193E-075 spec sheet for your reference. While it will be dimensionally identical, the torque and axial load capacities of the stainless version will be approximately half that of the steel version called out on the spec sheet. Note that these capacities are the absolute maximum that the particular unit will transmit, there is no safety factor built into the number.][/quote]

Not great, but Irving said that a chair is so far from the limits as not to be an issue, probably not a big concern.... :|

He asked me to call so we could discuss it further, and bottom line is that he said that estimated cost for two units in 316 stainless would be USD $5-600 :shock:

The standard steel unit was about $60.... Somehow I don't think stainless is worth 10X the price....

We didn't discuss costs, but he said they offered the steel units with either nickel or "Thin Dense Chrome" (TDC) plating with shorter lead times and no loss in strength...

Since we do have a powder coat setup for small stuff here at the Asylum I asked him if it would work to powder-coat the parts, as that would give at least some protection.... He said that he would need to check w/ their engineering dept. as he didn't know if baking the powder coat would cause problems... (they only rate use at up to 400*F)

Does the 10X price difference and long lead time for stainless sound reasonable, or should I check w/ some of the other manufacturers?

What about going with steel - would powder coat be reasonable protection? (After I tighten the units down, I might replace the screws w/ stainless....)

If not, other options for protecting against rust - or just not worry about it???

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Irving » 24 Aug 2019, 02:30

If Powder-coating you'd need to find a way to keep the mating taper surfaces free. Also the surface friction coefficient could screw up the numbers. I'd pass.

Personally I'd go with either the nickel or chrome finishes. Both are fairly rust resistant, look good and sensible pricing. And if they do go a bit manky after a couple of years just swap them out.
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 25 Aug 2019, 03:43

Irving wrote:If Powder-coating you'd need to find a way to keep the mating taper surfaces free. Also the surface friction coefficient could screw up the numbers. I'd pass.


OK... That makes sense and I'd thought of it a bit already, not just on the tapered mating surfaces, but also on the shaft and hub surfaces, since the coating would probably change the dimensions... However, my understanding was that you could keep powder coat off places you didn't want it by covering up the surfaces w/ Kapton or similar heat resistant tape?

Personally I'd go with either the nickel or chrome finishes. Both are fairly rust resistant, look good and sensible pricing. And if they do go a bit manky after a couple of years just swap them out.


Will have to look into pricing on the plated parts...
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Burgerman » 25 Aug 2019, 12:11

Or you can easily DIY with nickel. Remember my coins? Its simple and very quick.
User avatar
Burgerman
Site Admin
 
Posts: 46370
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: New Tyres on my Puma 40

Postby Mind The Gap » 26 Aug 2019, 13:41

Hi All fitting my Heidenau tyres on but cant remove key to slide washers on, any help please.
Cheers Paul
Otto Bock B500 with 105ah lifepo4 main, 48ah lifepo4 addon. 153ah total.
User avatar
Mind The Gap
 
Posts: 172
Joined: 02 Feb 2015, 21:37
Location: S.E London

Re: New Tyres on my Puma 40

Postby Burgerman » 26 Aug 2019, 17:10

You will have to, with screwdriver and small hammer. Or file notches in washers...
User avatar
Burgerman
Site Admin
 
Posts: 46370
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 28 Aug 2019, 20:44

Had another long talk on the phone this afternoon w/ another sales engineer from Climax Metal Products...

We talked about what I was trying to do and materials etc... He confirmed that my basic idea was very much within their safe operating parameters....

He did suggest that their C192E-075 assembly would work better for me - in looking at my spreadsheet it is very similar in most specs, and the ones that are different aren't all that critical... The BIG advantage is that the 192 stock unit is zinc plated so it gives some corrosion protection out of the box....

He then said that if I tape up the contact surfaces and screw threads, it would be OK to powder coat the exposed surfaces - no problem w/ baking...

He said that as long as I torqued the units up with the standard high strength screws, I could then take the screws out and replace them w/ stainless - better for rust prevention...

He even said they are on Amazon so I can use my credit card bonus points to pay for them.... cheers

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Re: New Tyres on my Puma 40

Postby Irving » 28 Aug 2019, 23:18

ex-Gooserider wrote:Had another long talk on the phone this afternoon w/ another sales engineer from Climax Metal Products...

He did suggest that their C192E-075 assembly would work better for me
.....
He even said they are on Amazon so I can use my credit card bonus points to pay for them.... cheers

ex-Gooserider

True, on Amazon.com, but not available on Amazon.co.uk. $72 each 1 - 3months shipping to UK! Or $176/pack of 3 but doesn't ship to UK. Or $61 on eBay.com...+ $25 shipping!
Puma 40, 75Ah LiFePO4
Spectra Plus
User avatar
Irving
 
Posts: 1405
Joined: 04 Dec 2012, 11:51
Location: NW London

Re: New Tyres on my Puma 40

Postby ex-Gooserider » 29 Aug 2019, 03:55

True, but I'm in US, so works for me... 8-)

For me they were USD $68 each, plus about $7 shipping on the first one...

Climax seems to be US-centric in their operation, even though they said they had the assemblies made at their plant in Italy... Their data sheets are also mildly annoying in that they are all in Inch measurements, even for their metric sizes... I can live with either one, but mixing gets annoying....

So now it's waiting a bit until they arrive, so I can confirm the measurements before redoing the drawing... (NEVER trust the data-sheet completely.... :ugeek: )

I do need to make one minor aesthetic decision - I don't think it would make any significant functional difference... The unit has a 'top-hat' flange that's about 1/4" thick.... While the hub obviously has to be long enough to cover the mating surface area of the assembly, it wouldn't be hard to make it a bit longer in the 'spigot' section so that I could cut a pocket to recess some or all of the flange...

Recessing the flange would not need much more than a couple of extra lines in the CNC file....

If the spigot ends up much thicker than the wheel, then there is also the option of beveling or rounding it over.... That would take a tool change along with the extra code, but not a big deal....

ex-Gooserider
T-5, ASIA-B
Jazzy 1100
Jazzy Select 6
Quickie Q-7
Invacare Mariner
Want to make / get a better chair, ideally one that stands.
User avatar
ex-Gooserider
 
Posts: 5126
Joined: 15 Feb 2011, 06:17
Location: Billerica, MA. USA

Previous

Return to Everything Powerchair

Who is online

Users browsing this forum: Google [Bot], ICEUK and 26 guests

 

  eXTReMe Tracker