New Vertex RT-Disguised backlash-?

[Chris MateParticipant @chrismate31303]

Hi, after completeing and threading the holes(a lot) on the Disc I made clamps(Various) 8mm bolt size for use to RT Vetex-HV-6 model, 3x slots.

Stops made:
I then decided to make two adjustable sliding stops which slide on the outher edge of the disc, bolted in place to privide working between two stops, milling curved slots 8mm  in it.
It is with this operation, I realised there must be some backlash as cutter gets to end of cut and excit, where conventional milling feels like climb milling exciting the workpiece.

Backlash experience on this RT by me:

1-If I move the the table normally by cranking, I feel no backlash, it feels smooth, if connected a dial indicator I dont see any, but this is light load.
2-If I mill I feel the possibility of backlash in handle, under load with cutter, I can feel the difference between climb & conventional milling here.

3-This brings met to completing the stops and adjusting the table towards a stop, and if table stopped at 0 degrees as example by two stops, disc/table no movement, I can detect definite backlash.

4-The “Manual/Pamflet I got with it is quality printed, and it says under “ADJUSTING MESH OF WORMGEAR” (Theres zero axial play=Another type of adjustment), it says theres a screw A-Steel Ball-Screw B to adjust this. On inspection I found one screw(A-?), no steel ball, no screw B, if A is screwd out, I can see the conentric part turning inside.
Screw A=12mm long by 4mm allen.
Now whatever I try I cannot get this backlash adjusted out……I can adjust it where it feels uncomportable stiff to turn, but the backlash still theres.

Its not the end of the world, but just curious what you think. I am going to enquire as to where the ball & screw B is from seller.

Thanks for ideas……This backlash confuse me a bit….

[JasonBModerator @jasonb]

Screws and ball shown on the exploaded view, ball may be stuck in grease. Effectively it is a stop that adjusts where the eccentric stops when you turn the lever to swing the worm into mesh.

 

[Chris MateParticipant @chrismate31303]

Hi, If I loosen the T-Handle to release, If I feed(Try to) the dial with my hand and adjust that one screw in or out, I can see the dial moving, so there is only one grubscrew, no ball and screw B further down in. I can see the part unrestricted with light shine in 4m hole, so not sure if they change it on new one, or just a miss assembly, waiting for answer from dealer.

So the one screw(A) 12mm long does change the backlash to a point where you get no backlash under no load like against a stop, or cutting, it indeed feel very smooth and good cranked with no load, I can adjust where it feels stiff to turn, but I can still produce the backlash againt a stop-?.
Not sure if the main tapered bearings(maybe slight play, cannot feel anything by hand) can cause something like this-?

Its not like on a Lathe or A Mill where you can feel the backlash with no load, easy.

[DiogenesParticipant @diogenes]

There has to be some ‘space’ between the moving parts in any mechanism.

You cannot rotate a (300Euro) worm/wheel rotary table up to a stop in one direction, and then ‘back it out’ in the opposite direction without having some backlash at the point of reversal.

Maybe one reason why they don’t have stops as standard.

BUT.. ..the backlash can be minimal / you can use the locks to ‘damp’ it / withdraw the tool / rotate the table manually instead of by handle…

There are a number of ways of achieving a desired result, what is the operation that you are trying to perform – why does the backlash matter?

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Diogenes makes an excellent point !

Without wishing to push this Topic too far astray from its spirit … I suggest dipping-into these pages:

https://sextantbook.com/category/chasing-tenths-of-an-arcminute/

The site is a master-work, and although a lot of it is not directly relevant to ‘Workshop’ rotary tables … all the fundamentals are there.

MichaelG.

 

[Michael Gilligan]

On Michael Gilligan Said:

Diogenes makes an excellent point !

Without wishing to push this Topic too far astray from its spirit … I suggest dipping-into these pages:

https://sextantbook.com/category/chasing-tenths-of-an-arcminute/

The site is a master-work, and although a lot of it is not directly relevant to ‘Workshop’ rotary tables … all the fundamentals are there.

MichaelG.

 

Hi, I understand backlash as I dealt with on mill as example, however as 1st time user of a rotary table HV-6(Small), I was a bit surprised at what I perceived it to be and what I experience as I was actually milling on it.

So I was milling a curved slot at the outer edge of the 200mm dict added to the 160mm table to have more space.
-My perceived backlash was theres nothing or very little, I cannot measure or feel it by turning the table without milling on it. On the mill theres no doubt.
-So imaginge you using a 4 Flute 8mm cutter to enter the workpiece from either side, with both entry points not square, IE the cutter 1st cut with one side a few mm, then it cuts the slot both sides till the other end is reached, then it leave the part by cutting again on one end few mm.
It was at either ends , no matter wich direction I turn the table, it gives the impression of limb Milling, slightly feeling it wants to run away(Feel in handle)=(Now you feel the backlash under load at play), and it does not matter from wich side you start.
-Milling slot in the part after cutter touches/cut both sides its very stable feels very good.

So I started looking into this as a result of above experience versus my initial perceived to be experience I though I was going to get.

xx-The interesting part for me was that I could adjust the backlash as the manual stipulate, and reach a point where its feels not right=Too stiff in turning, but at that point it still has backlash if forced with a stop.

xx-So it was the difference in measuring thebacklash without a stop with dial indicator & feel, versus a stop or locking the table.

Note:
I found some info where they actually test CNC milling tables by forcing it and then have a spec that permit X-Backlash repeatable, they crank it by X-Force to determine, and that figure is somehoe taken into account in machining.

Note:When I made the Aliminium disc and milling the outer edge of it with conventional milling, turning the table right into/againt the cut It feel cutting strong, no problems, but that was a different one sided 4-Flute cut than in this case entering exiting a workpiece for few milimeters.

I will post a photo later of how it was clamped down and you can see the slot milled.

[DiogenesParticipant @diogenes]

Ah, yes, I think I understand.

A cutter will give some (un)funny effects as it enters and leaves the work because incomplete engagement forces the tool sideways – a workpiece bigger than the table will really let you feel the ‘pull’, it should be controllable with care, sometimes it is prudent to slow the feedrate at awkward entry & exits.

Another issue with stops on a R/T is that the low gearing of the worm-drive mechanism provides enough force to overcome/stress the stops – it’s very difficult to achieve good repeatability because of the lack of direct feedback at the handwheel – you cannot feel whether you are just touching the stop, or ‘driving over it’ by 0.1mm.

To ‘work between stops’, I use a small manual table with no worm drive.

 

[SillyOldDufferModerator @sillyoldduffer]

Don’t expect too much of backlash adjusters on ordinary equipment.

My lathe cross-slide has a slot cut across the nut that can be tightened with a screw so the nut bends to grip the lead-screw on both sides.   The arrangement reduces backlash rather than eliminates it, and comes with a major disadvantage!   A tight slot minimises backlash at the cost of high friction and severe wear.   With this system,  it’s better to tolerate a little backlash, and compensate for it manually.   Constantly adjusting the slot for no backlash is more trouble than it’s worth.

There are anti-backlash mechanisms that work without causing wear and tear, but they aren’t simple or cheap!  None of my equipment  has a well-engineered anti-backlash mechanism.   Instead, I have to manage backlash myself.    It’s a nuisance that slows me down, rather than a serious problem: I seem to manage somehow!   Every so often I forget, causing ‘industrial language’ and bad tempered stomping off.  A glass of wine helps…

Dave

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