Thanks: 1
Likes: 1
Needs Pictures: 0
Picture(s) thanks: 0
Results 1 to 13 of 13
Thread: Can I make shafts for my CNC
-
8th April 2014, 01:41 PM #1
Can I make shafts for my CNC
I noticed that the gantry on my machine was jerking a little when I was stepping it very slowly with the pendant. I thought 'bigger' (but used a 'u' instead of an 'i') looks like a bearing has had it. So I undid a few bolts and slid the bearings off the end of the shaft. As I did, all its little balls fell into my hand. So I decided that I had better look at the other one as well and that too poured out.
Luckilly, I had a couple of spare bearings in stock so got them out thinking that I would just swap them over and start up again. But then I wondered why the originals bearings had both become so discombobulated. On inspecting the shaft I found numerous little marks the length of the shaft and realised that the shaft itself had been damaged by the bearings.
So,
I would like to make some new shafts for my CNC machine but I will need help from some knowledgable engineering person.
Firstly I would need to know what type of shafting to buy for a rail that is 20mm * 2000mm.
Secondly the rail needs to be able to be machined using a standard pedestal drill so that I can drill and tap for the support rail attaching holes prior to getting the shaft hardened.
So I need to know first off whether it is a practical thing to do and then whether the costs involved would be greater than just buying another shaft from China.
Your thoughts would be appreciatedBob Willson
The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.
-
8th April 2014, 01:46 PM #2GOLD MEMBER
- Join Date
- Jul 2006
- Location
- Port Huon
- Posts
- 1,917
It would be cheaper/easier to just buy a length of hardened 20mm shaft rather than make your own.
$50 plus shipping on eBay.Geoff
The view from home
-
8th April 2014, 03:00 PM #3
If I buy hardened shaft then I will not be able to drill and tap the holes for the support rail attachment.
Bob Willson
The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.
-
8th April 2014, 03:06 PM #4GOLD MEMBER
- Join Date
- May 2003
- Location
- Perth WA
- Posts
- 999
Bob,
You will never drill through that rail with standard drill bit. I have broken drills and taps in that material trying to fix rails that were out of wack.
It sounds to me like your original rails were either stainless or not case hardened to have worn a bearing track down the length.
Same seller as Geoff pointed to but the complete rail.
http://www.ebay.com.au/itm/SBR20-200...item43c3a60813
Perhaps your gantry weight is too heavy for the bearings you have so maybe think of adding more bearings to distribute load over a larger area.Cheers,
Rod
-
8th April 2014, 03:24 PM #5GOLD MEMBER
- Join Date
- May 2003
- Location
- Perth WA
- Posts
- 999
Bob,
You could also look to the long linear bearing if you think it would be better. I know this link is for a 16mm and you have 20mm but I'm too slack to find you a 20mm one.
http://www.ebay.com.au/itm/SBR16LUU-...item46170147c2Cheers,
Rod
-
8th April 2014, 03:33 PM #6SENIOR MEMBER
- Join Date
- Feb 2008
- Location
- Australia
- Posts
- 162
Can you flip the bearings around and reuse the rails or are they damaged beyond use?, flipping the bearing 180 degrees should offset where the ball bearings touch the rail.
-
8th April 2014, 06:43 PM #7
Hi Rod and Chris
Thanks for the input.
The original rails were from China from Chai and so they are actually both case hardened and chromed. They are very hard, but the bearings are harder still and so the shaft suffers before the rail. This rail has been replaced before for almost exactly the same damage.
My gantry and motors (4 motors all up) (2 spindles and 2 steppers) weigh about 60Kg between them, so it is possible that you are correct in your assessment. I had looked at that rail from cupcake with a view to replacing the existing rail with that same one. I had not thought of using a longer bearing, but I can see that it would be beneficial to my cause.
I am not sure Chris that the bearings are able to be flipped as you suggest. I will test it tomorrow. At present, the rail on one side has suffered quite a bit of indignity, but if the bearings will actually bear on a different area then that may be a less costly solution.
I am also pondering the advisability and costs of swapping both rails to use 20mm Hiwin rails instead. This would cost about $800 ($260 for the rails and $170 for the bearings) and so it is not an inconsequential expense. On the other hand, the rails would then be practically indestrucible and of much superior quality.Bob Willson
The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.
-
8th April 2014, 08:16 PM #8
The issue with making your own rails including drilling and tapping material, then hardening them is that they will distort during the heat treatment process and will require a final touchup regrind get them dead straight. This will leave them marginally undersized for the bearings, affect bearing contact areas, and certainly cost more than replacement units.
I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
-
8th April 2014, 10:22 PM #9SENIOR MEMBER
- Join Date
- Sep 2009
- Location
- Newcastle
- Posts
- 516
Have a look at hiwin linear profile bearings from BST automation on aliexpress. They are very well priced, haven't bought from them personally but a few good experiences on cnczone. Profile bearings are a massive upgrade over round rails.
15mm profile rails will be more than strong enough.
-
9th April 2014, 01:28 PM #10
Hi pippin88
Those are the rails that I would like to use but I am unsure of the benefits of the wide carriage bearings as opposed to the narrower type. Can any body throw any light on these please?
I know you say that 15mm rails would be fine, but I always prefer to overengineer things, so I would probably go with 20mm rails if the price difference is not too great.
This one from CYS Bearing would do the job. I don't know if these rails are all made by the one manufacturer (hiwin) or whether individual companies make them to Hiwins specifications.
BST Automation seem to only sell in sets of 4 rails
Even with paying the huge freight costs from China to here, it is still a lot cheaper than buying here.Bob Willson
The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.
-
9th April 2014, 04:29 PM #11GOLD MEMBER
- Join Date
- May 2003
- Location
- Perth WA
- Posts
- 999
-
10th April 2014, 12:46 AM #12
This price is half what the same thing purchased here would cost me. ($860 for the 15mm rails and carriers)
If it weren't for the killer air freight, it would have been only 1/3 of the price here
http://www.aliexpress.com/store/809194
Sometimes I worry that I am being faithless to Australia and the economy, but then I ask myself why I think that. The shops here buy from overseas just like we do but they add on huge profits for themselves, so why shouldn't I avoid the middleman and buy what is best for me.?
2000mm linear guide rail HGR20 HIWIN from Taiwan 2 pieces $172.20
linear guide HGH20CA HIWIN 4 pieces $ 85.48
Product Amount Shipping Cost Total Amount
US $ 257.68 US $ 224.89 US $ 438.00Bob Willson
The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.
-
10th April 2014, 01:28 AM #13GOLD MEMBER
- Join Date
- May 2003
- Location
- Perth WA
- Posts
- 999
Bob,
No need to feel guilty as the retailers in Australia charge what they can get away with and it has nothing to do with reasonable profit. While they are servicing the resources boom their profits are multiples of an overseas retailer. Note I said retailer and not manufacturer. The irony is they look for protection if they loose sales to individuals willing to procure overseas and in this case it's not like you are taking away onshore manufacturing opportunities.
The rails are 2m long so the high cost of air freight is to be expected.Cheers,
Rod