I want to DIY.. some questions please!

**JAZZCNC** · 30-03-2012

Originally Posted by Tenson

Is there a big advantage in build quality terms using profile rails for the Z-Axis rather than supported round rail?

I must admit I can't see an easy way to use supported rail so that the bearings oppose each other on the Z axis. I have seen Jazz used HiWin rails facing out, not opposing, so is this only okay with profile rail?

The advantage of profiled rails are much tighter bearing tolerences with a smooth action helping to reduce resonance and flex they also last much longer, esp in harsh conditions like a Z axis where it's constantly in the firing line and open to crap from the cutter. They don't really add much more strength than supported round rail if any.!

You can use supported rails just the same as profiled like you have seen me do. Absolutely no difference other than they stick off the Z axis rear plate (which you would call running across X axis, me Y axis) slightly more due to height of supported rail.

**Tenson** · 30-03-2012

Thanks I rather thought it might be the case, though good to know open bearings on supported round rail are not a no-no. The HiWin rail is okay priced but the bearings seem a bit steep. How about other brands? RS Components sell one called IGUS DryLin T which for 300mm is quite affordable (GBP14 rail, GBP16 Carriage, I can't do the pound sign on this Korean computer) but doesn't offer longer rails. There are many other brands too.

**Tenson** · 16-04-2012

Hi Guys,

I got some SBR rail from CNC-4-U with open bearings. The bearings look like they are normal ones that have been cut open. Is this normal? They also have little grub screws in the top that hold the bearing in and when tightened up they close the bearing up on the rail a little. The motion was a little jerky at first but after a quick sanding of the cut endge of the bearing thye are smooth now. They seem a bit home made. Should I be sending them back or are they okay?

**Jonathan** · 16-04-2012

Originally Posted by Tenson

They seem a bit home made. Should I be sending them back or are they okay?

That's perfectly normal. Same as you'd get from linearmotionbearings2008 on eBay. I ordered some recently from china (not for myself I hasten to add!) and they came in less than a week. The're essentially the same except the grubscrew is now on the side of the bearings, not on the base.

**JAZZCNC** · 16-04-2012

Personally I hate these bearings they are rubbish.!
There hardly ever flat or square making mounting without binding difficult they go sloppy on the rail in no time, they wear like crazy if you operate them in any reasonably dusty or abrasive conditions.

Do your self a favor and save up for some real profiled rails or at least buy some decent bearings and blocks, to me it's just false economy because if you build a decent machine frame these will quickly become the weak link and you'll want to change them and it's not often a quick swap over job to change to profiled rails.!! . . Spending on profiled rails is one area where I promise you won't regret or begrudge the extra expense.

**Tenson** · 16-04-2012

Thanks for that. I like CNC-4-U. They are UK based so I'm supporting local trade and the prices are not too far from the eBay ones. I got the 2.2KW VFD spindle and 4Nm steppers from them too.

Jonathan, can you link me to some more pictures of your machine? I saw it in the video for the single flute cutters but I'd like to see more detail.

**Tenson** · 17-04-2012

Hi Dean, I thought about profile and besides the cost, it seems like it would be more fussy about the surface they are mounted on. I don't have the ability to machine the mounting surface 100% flat, so I think the stiff supported rail will help there. I have to say I'm not very impressed by these bearings though. Can you recommend some higher quality open bearing for this type of supported rail?

**JAZZCNC** · 18-04-2012

Originally Posted by Tenson

Hi Dean, Can you recommend some higher quality open bearing for this type of supported rail?

Sorry didn't see this post. Other than Gary at Zapp then no not really because I won't touch them personaly and I only ever come into contact with them when others have all ready bought them. I hate the bloody things because I'm always having to machine them flat and true even then there still left with shite bearings.!!

Said it before many times but If you want real accurecy and longevity then get rid and save for some profiled rails and don't even go the unsupported route because you will regret that path promise you that.!!

**Robin Hewitt** · 19-04-2012

Originally Posted by JAZZCNC

If you want real accurecy and longevity then get rid and save for some profiled rails and don't even go the unsupported route because you will regret that path promise you that.!!

Ah! Someone with experience of Hiwin rails

I'm drawing up a plasma cutter with a 2 meter axis on the gantry and I want to use one profile rail, probably the 20mm.
My problem is the spec says they come in two flavours...
1: with slop to allow for slight misalignment between 2 rails.
2: with oversize balls to get a tight fit.
Zapp seems to sell only the sloppy variety and I can't afford twist around the long axial because the head sits quite far forwards, about 65mm ahead of the races.
My question is, how much axial twist do I expect?
Should I add a spring roller running on the rail behind to keep it in tension? That wouldn't be hard because I have to screw the rail from behind so there are no visible holes that might carry abrasive crut passed the wipers.

**Tenson** · 18-04-2012

I must say I'm starting to wonder if I will just use the unsupported rail. The bearings seem much smoother and tighter tolerance! It's all very well having stiff rail, but I can find some places on the supported rail where the bearing will wobble slightly side to side.