lead screw diameter for 6 ft table

[tkms002]

Doing the research for building a router table and I was looking for advice for the lead screw diameter for a 6 ft table?
I know whip can be a problem on long spans so I was also wondering if anyone has ever tried floating midspan bearings to stop the whip. What I envision is an additional bearing on each side of the nut attached to the table on something like a drawer slide so when the nut runs into it it just slides along with.
Bruce

[Pplug]

My Techno lc4896 has those slides built into the x axis and has about a 16mm diameter screw 7 ft long. The small plastic spacers slide in the same channel that the ballscrew lies in. I think that the lead is close to 5 mm a turn and with the right motors and controller, the axis can move at speeds over 800ipm! I bet that without those spacers the ballscrew would whip itself do death at much lower speeds.

[RossMosh]

Any reason you are not going with an R&P system?

[tkms002]

Haven't realy thought about it. Just started looking into this a week ago. Mostly I want a machine that can cut thin aluminum in long pieces and profiling thicker aluminum in smaller pieces(bearing blocks etc). Robot parts.
Then wood and other materials come after that.
What do you think I should do in the long axis.
Bruce

[Pplug]

You might ant to look into some ballscrews from chinese sellers. I think they are more accurate and provide greater transfer of power from the motors. Leadscrews are about %60 efficient and R&P is about the same.

I just bought the following:

3X 53" 1605 ballscrews with endmachining
1X 18" 1605 ballscrews with endmachining
mounts for both ends of all ballscrews
flexible motor connectors
4X 53" 20mm linear bearings with 8 bearing blocks
2X 18" 20mm linear bearings with 4 bearing blocks

All for the price of $960 shipping included! I also purchased a 2 spindles from the same person, one was about 2 years ago & still working!

The best part of the whole deal was that all the components were bolt on ready! No finagling needed. The parts were delivered about a week from placing the order.

The machine is almost done, all I have to do is connect the electronics.

[RossMosh]

Originally Posted by tkms002 Haven't realy thought about it. Just started looking into this a week ago. Mostly I want a machine that can cut thin aluminum in long pieces and profiling thicker aluminum in smaller pieces(bearing blocks etc). Robot parts. Then wood and other materials come after that. What do you think I should do in the long axis. Bruce

A lot of people use the R&P system cncrouterparts has. There are other people who prefer to use v-groove bearing like in Joe's 4x4 Hybrid.

The main issue with ball screws and lead screws is dust and expense. Ball screws are more sensitive to dust than R&P. That's not to say you can't keep dust of the screws, it's just more important than in a R&P system. The other issue is to get a "whipless" screw setup, you need to get the right size/quality screws. This can become an expensive purchase.

It wouldn't surprise me if a build like Pplug's made people look at using ball screws more seriously in larger tables. It also wouldn't surprise me if Pplug had similar issues as others have had with ball screws.

To summarize things, ball screws, lead screws, and R&P all work. R&P seems to be the easiest and most cost effective method for the DIYer on the budget building a larger router.

[Pplug]

The ballscrews I use have a rubber wiper that rides in the chanels of the screws effectively sealing them from debris on the insides of the nut. It is also replaceable if you need to change it. The same goes for the linear bearings. Rack & pinion would be ok exept you don't get the accuracy or repeatability that you would with the ballscrews. To be honest I've only seen one machine that used r&p and it was not that impressive. I'm sure I'm biased tword ballscrews but all 4 of my machines have them on all axis and have excellent results.

The same people I bought my stuff from sell larger diameter screws for not much more.

[tkms002]

pplug who is the chinese seller?

[jsheerin]

I'd use rack and pinion personally, but there is a guy selling ~100" long Hiwin rotating nut screws on ebay right now for $200. I think his add said he had 40 of them.

[Pplug]

Here is the sellers store:
linearmotionbearings items - Get great deals on items on eBay Stores!

I got a better price not going through e-bay but still using paypal for purchasing. I thought it was risky at first but they have been extremely reliable for my multiple orders. If you don't find what you like, just ask him for a quote from any of his auctions and he will respond within a day.

[MaxMekker]

Can also recomend Linearmotion2008 seller.
I bougt 20mm screws from him (outside Ebay) and they work perfect.
My screw is 1380mm(54+ inch) long and have no problem with whipping.
One thing to think about is the pitch on the screws, high pitch and you don't need high rpm and you keep the torc on the steppers.