# Sliding table deflection



## petertha (May 10, 2020)

I'm not a CNC guy but I have an idea for a machine accessory to mount to my lathe cross slide that could utilize one of these offshore sliding tables. What I'm trying to figure out what kind of deflection one could expect if a tool was mounted normal to the sliding block (red line) and cutting forces would apply the equivalent of a torque to the dual slide rod assembly (orange arrow). Unlike a typical dovetail configuration on lathe or mill, it looks like these CNC tables float on the 2 slide rods, there is nothing contacting the slide to the frame (green arrow). This was just an Ebay screen grab but do companies provide a deflection spec in this manner? I see what I think are similar assemblies holding the spindle motors in CNC routers so assume it has to be 'pretty' rigid as its milling laterally through material. But how much force & how much deflection I wonder? Any references or rules of thumb you can pass on?


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## matthewsx (May 10, 2020)

The serious bearing suppliers provide all kinds of data about their products, ebay sellers not so much.

What type of application are you thinking about?

John


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## JimDawson (May 10, 2020)

Those rods will have a lot of flex, only supported on the ends.  The do make those linear slides with rails that are screwed to the base, a much more robust system.









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## Asm109 (May 10, 2020)

1/4 inch rods or 1" rods?  Thomson makes the rods and bearings and they have lots of engineering info, start digging


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## petertha (May 10, 2020)

One is holding a grinder spindle and traversing along a length of rotating stock. So I suspect lighter lateral load but any flex or harmonics might be magnified into not-so-good finish & accuracy issues. Another might be like a regular tool post  mounted to the slide but (light duty) cutting along rotating stock. So higher lateral forces. Maybe as a visual, the lathe compound is removed & sliding table mounted to the cross slide. The table could be mounted at desired angles relative to the lathe bed or at different positions on the cross slide depending on the application. (Yes, I know, conspicuously like a taper attachment LOL). Another is more or less a standalone application where I need to traverse.

JimDawson, I was looking those linear slides too but know even less about them. I assumed they must be on a track of bearings so maybe a whole bunch of individual point loads? (I really don't know what I don't know lol). Any links would be educational.

Kind of interesting to me. Dovetails are kind of ubiquitous on cutting machines because they slide & they contain heavy forces. Yet there doesn't seem to be available 'modular component's to make up assemblies, like male & female dovetail slide strips to mount to blocks. Everything is cut from solid castings integral to the machine itself.


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## JimDawson (May 10, 2020)

petertha said:


> JimDawson, I was looking those linear slides too but know even less about them. I assumed they must be on a track of bearings so maybe a whole bunch of individual point loads? (I really don't know what I don't know lol). Any links would be educational.











						CNC Electric Sliding Table Linear Stage Cross Slide Module 1605 Ballscrew 500mm  | eBay
					

Find many great new & used options and get the best deals for CNC Electric Sliding Table Linear Stage Cross Slide Module 1605 Ballscrew 500mm at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				












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## matthewsx (May 10, 2020)

I built my CNC machine with linear guides and they are very robust, here's some info from NSK who make high quality stuff.



			https://www.nsk.com/common/data/ctrgPdf/e3332b.pdf
		


Good deals can be had on eBay if you're patient, I looked at the new units from overseas but ended up getting a used X-Y stage that was US built.

Cast iron dovetail components are available but you really have to search for them, I found a supplier a while back but sizes and pricing were out of my league. 

Actually, linear rails are what's used in most production equipment these days because they are modular, can be sourced in so many different sizes and configurations, and don't require specialized labor to scrape them into accuracy.

John


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## petertha (May 10, 2020)

So you're saying in principle I would be better off looking for a linear rail guide assembly for better support vs the twin slider rod assembly. And where a lead screw goes through the block if I want to hand crank or drive it.






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## JimDawson (May 10, 2020)

petertha said:


> So you're saying in principle I would be better off looking for a linear rail guide assembly for better support vs the twin slider rod assembly. And where a lead screw goes through the block if I want to hand crank or drive it.
> 
> 
> 
> ...



The one I linked to above would be more stable, has dual rails.  The single rail unit would be pretty stable, but not as good as dual rails.  Linear rails can take a lot of load in any plane.  I'm sure you can get one shorter than 500mm if you need it shorter, or just cut to length.  I'm going to purchase a 1500mm unit pretty quick for an upcoming project.


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## petertha (May 10, 2020)

Ah, I completely overlooked that detail. I see the 2 from the underside now.


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## JimDawson (May 10, 2020)

petertha said:


> Ah, I completely overlooked that detail. I see the 2 from the underside now.



Ya gotta read the fine print


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