Gearcutting

[Dinkum]

Hi all,

Would anyone know whether this rotary table would be ok (rigid enough, etc.) for cutting gears (up to about 6in) ? : http://www.machineryhouse.com.au/R001

Also, is the degree of turns (IYSWIM - 10 minutes in this case) small enough for most teeth numbers? (i.e. 52 teeth)

Thanks from a newbie. I hope the question isn't too stupid or generic...

 

[dgjessing]

That looks exactly like mine, which I got from Harbor Freight. It's useful to a certain extent, but I wish I had gotten a better one. It lacks a precise center bore, so it's not an easy matter to exactly center a chuck on it. Has quite a bit of backlash too...

 

[mklotz]

Does it have provision for mounting hole plates for doing indexing? I ask because ten arcminute divisions seem a bit coarse for gear making.

As an example, a 52 tooth gear on a 36:1 table requires you to move the table handle through

36/52 = 18/26 = 9/13

revolution between teeth. One handle rotation is 600 arc minutes so the required movement is:

600 * (9/13) = 415.3846... arc minutes.

How well do you think you can dial that in on a scale with markings every ten minutes?

Moreover, looking at the detailed pictures on the H&F site, there appears to be ten major divisions on the handwheel (i.e., 10 deg) with each major division divided into four subdivisions. If that's true, each minor division is 15 arcminutes, not ten.

If it were my choice, I'd hold out for a proper table with the ability to use dividing plates.

 

[maury]

Hi, When I started cutting gears on a mill, I used a Phase2 spin index, made appropriate arbors for the gears. I used a large diameter piece of drill rod and turned down the end to a snug fit for the hub. Use a thick washer and a screw to hold it tightly in the arbor. This worked ok for gears up to about 3" or so in bronze with light cuts.

If you need to go bigger you will need a much more rigid system. My advice is not to bottom fish on price when buying a rotary table. I have a Phase2 8" I'm happy with. Using that you can add a 3 or 4 jaw chuck to hold your work and with light cuts you can likely be successful with 6" gears in steel.

I use a Barber Coleman hobber now, and for gears 4" or larger, I use a work arbor made from 1 1/8 drill rod and use side supports about 1/4" under the pitch diameter for support.

Hope this helps,
maury

 

[Blogwitch]

If you are wanting to do fairly accurate RT work, then you really need to invest in a table that has at least a good vernier scale on the handwheel. The one you have shown is a very basic unit. OK for a bit of none too accurate machining, but really not good enough for precision work.

If you are limited to size, then the Vertex 4" or one of it's many clones is what you should really be aiming for.
Those also have the capacity later to turn into a basic dividing head, using plates and fingers, without spending too much extra cash.

Original Vertex

http://www.chronos.ltd.uk/acatalog/Vertex_Rotary_Tables_and_Accessories.html

A very good, and much cheaper clone

http://www.chronos.ltd.uk/acatalog/Soba_Rotary_Tables_and_accessories.html

And a dividing set that will fit either table

http://www.chronos.ltd.uk/acatalog/XMAS_GIFT_IDEAS_4.html#aXC168

I am not saying you have to go this way, I'm just showing you what you should be aiming for if you want to do really accurate work with an RT.


John

 

[purpleknif]

Problem I have is clearance under the head.

 

[Maryak]

If as you say gears up to 6", that table is not going to be rigid enough in the vertical position and the handwheel for the worm drive is going to be in amongst the mill head assuming you have enough z travel.

Forgive me for saying that your $95 would be better left in the bank.

I guess the short answer we have all given so far..............no..........it is not good enough.

Best Regards
Bob

 

[Herbiev]

I agree with the Bob. If you were to cut a 6" steel disc say 5/8 or 1/2 thick using single point gear-cutting this unit would be far too flimsy. At the very least go the next size up (110mm). At least it has a MT2 centre and from the picture seems a little sturdier. Good luck in your search.

 

[tel]

I have a 4" almost identical to that - OK for some things, well, quite a lot of things really, but not something I'd attempt to cut gears with. I ude my handy dandy Harold Hall simple dividing head for that.

 

[ShedBoy]

I looked at one of these yesterday while I was at their shop. You will not get the accuracy to make a good gear as it sits. If clearance is your problem can you raise the colum at the mount (this I need to do with my bridgeport clone when I can find a ring kicking around) You can get a set of dividing plates for it for another $120 product number R016 which would help greatly but does require an adaptor to be made and fitted. There is a brochure showing how it is done. The plates are off a 6" table so you wil either have to set the plates and handle over the edge of the table or raise it up which will not help. That said it could be done but would require low loading when doing the cuts, gashing first with a slitting saw. Hope this helps.

Brock

 

[Dinkum]

Hi all,

Thanks for the replies. I think when I go for one I'll get this: http://www.machineryhouse.com.au/R006

Now for finding the spare money.

 

[vcutajar]

I have one just like that and it is rock solid. Only problem is that many times I wish the table had four slots instead of three.

 

[Mosey]

What is it with RT's and their poorly arranged mounting slots, etc.? Some don't reach the inside of the table closely enough, and some don't have enough or rightly located slots, etc. Can't we do better? Especially the smaller ones are a problem in this regard. Or, is it me asking too much. My little Sherline is fairly good to mount to, but sure would like better one.

 

[mklotz]

A sacrificial table of diameter larger than the original RT table is always a good idea. Not only do you get more clamping area but you can pepper it with as many slots and tapped holes as your little heart desires.

 

[Mosey]

Ubiquitously informed, Marv, as always.

 

[John S]

I also have one of these tables and the original post was "gears up to 6"? and the answer is categorically no
just not rigid enough.

 

[lensman57]

Hi all,

Would anyone know whether this rotary table would be ok (rigid enough, etc.) for cutting gears (up to about 6in) ? : http://www.machineryhouse.com.au/R001

Also, is the degree of turns (IYSWIM - 10 minutes in this case) small enough for most teeth numbers? (i.e. 52 teeth)

Thanks from a newbie. I hope the question isn't too stupid or generic...

Hi,
I have the one you have shown and something from the arc euro trade ( slightly better built with a better vernier scale). They are ok for cutting small gears ( model engines and so on) if accuracy is not paramount. For cutting 6" gears with a reasonable degree of accuracy you need to invest in some serious RT of at least 8" diameter and these are pricy to say the least. These little RTs will not do.

Regards,

A.G

 

[hopeless]

A dividing head as per Tel's post will do the job well. I reckon its the best option if a RT is to pricey at the moment.
Pete

 

[electrosteam]

I agree with vcutajar that the 3 slots are a limitation.
I have a HV-6 and I have made dedicated slot nuts and slot nut extensions to extend clamping options.

My RT has an incorrectly engraved vernier scale, not a real problem once you get your head around the error.
Check that the vernier scale spans exactly 2 degrees on the main scale, return to supplier if not the case.

You don't need divider plates at first, just divide 360 by the number of teeth in Excel, write a conversion algorithm to convert the decimal part to minutes and seconds, and print out the table to place next to the mill.
Then each tooth becomes an absolute set point, not an increment from the one before.

John.

 

[Maryak]

Sorry John,

But if it's gearcutting then you do need dividing plates. The vernier on a rotary table is IIRC at best 10 secs of arc on the larger tables, on my Vertex 6" it is 20 secs.....so say 49 teeth

=360/49, = 7.346938776 deg = 70:20.081632653':48.97959184" rounding gives 70:20':49" or at best say 50 secs, then the error = 1.97959184*49 = 97 secs or 1.616 mins. On my Vertex the error is a minimum 8.979 secs or 7.34 mins!

I don't think you can afford the error the vernier will give for gearcutting.

Best Regards
Bob