Fabricating a TS arbor: - Specs?

[jon hamer]

Last fall, acquired a "new" 1988 Invicta Delta RT-31 10" scoring panel saw (3hp). This is my first and only real table saw. I got it for next-to-nothing at a liquidation auction, it appeared to have never been run (or fully assembled).

The arbor is short; set up for 20mm bore regular blades only. I intended to use a bushing on the 20mm arbor to run a 1" bored Forrest blade (have it). The saw originally came with an arbor extension - which is missing and no longer available from Delta. I originally wanted to have an arbor extension fabricated, but since I've got it apart - I'm wondering if I should just go for a whole new arbor - a regular 5/8" arbor.
First: Does anyone know if any of the metric table saws have arbor extensions that might fit my 20mm? This would be a simple solution.
If not:
I'm looking for the specific dimensions for a standard 5/8" arbor of sufficient width to run a 29/32" dado stack (or even 1" wide) and still be set up to run regular blades. I am planning to take my arbor specifications to a machine shop, and have it replicated exactly, except for the actual threaded end. What size threads do I go with? Where can I get the blade washer and nut for a 5/8 arrangement? (It's a RIGHT tilting saw.)
What metal should I use? How are arbors hardened/tempered? Is it a good idea to have it magnafluxed or tested for flaws otherwise? I expect that once I get a drawing of exactly what I need, SOMEONE can make what I am looking for, but I've got to know what I want before I go looking.

Thanks for your help
Jon Hamer, New to the 'Creek.

[tyler mckenzie]

i own that same saw, and use 20mm bushing. Mine also came with the 1" arbor adapter, it makes the saw really howl so i don't use it very often.

All i can suggest is taking your arbor out and bring it to a machinist. Modifying or making a new one, i can't tell you which route to take. Maybe try owwm dot com for suggestions.

[jon hamer]

So far, my biggest sticking point is that I don't have any dimensions for a standard 5/8" arbor. Has anyone got any ideas as to where I can find a measured drawing?

Thanks,
Jon Hamer

[Wes Grass]

Off my Dewalt portable:

Arbor is .624 dia, about 1-1/2" long. Thread is a square or Acme profile, about 1" long. Hard to measure the pitch down in there, but it's about 12TPI. The point to this is it gives the threads a flat top to support the blades. A V-thread would be sloppy, as they're typically .005 or so undersize.

The spacer is about 3/4" thick, and about 2-1/2" dia. Washer is 1/4" thick, same dia. Forgot to measure the thickness of the nut.

I'd use pre-hard 4140 for the arbor. Should be hard enough to resist wear, but won't snap off if you hook something hard into the blade. Cutting an Acme thread isn't a huge deal. The nut will be a bigger problem. McMaster only has 8TPI, which would be OK I guess as the grooves are narrower than a typical dado chipper. Might be marginal with a saw blade. The machine shop can make a finer thread nut, and the other pieces as well, but it's probably going to be expensive.

I can check dimensions on a Sawstop at work, but it'll take me a couple days to get over to another building (assuming I remember in the first place). If you can duplicate that, or a Unisaw or whatever, you can probably buy the nut and spacers for a lot cheaper than getting them made. Problem is you have to know exactly what the thread is.

An alternative method is to use a V-thread, but do it as a custom diameter to create the flat top threads. That requires a custom nut as well. If you go that route, have them make a couple extras in case you lose it.

[Chip Lindley]

Jon, there is no such thing as a *Standard* 5/8 arbor. There are many imported clones of, for instance, Unisaw arbors, but don't bet they all match in all dimensions. I sincerely doubt that any other arbor will fit your saw. Since your RT31 is a *specialty* saw, designed for scoring and cutting sheet stock, you will have to have any new, longer arbor fabricated, IMO! A custom milled arbor for your saw will NOT BE CHEAP! Getting a firm quote may cause you to form a Plan B quickly!

IF you do not plan on using the saw for its intended purpose, I am SURE you can make a handsome profit off the sale of the saw, and buy a 10" or 12" saw more suited to general woodworking! Sometimes its easier and wiser to trade up than to modify! For the cost involved, you could sell the RT31, buy what you really want, and live happily ever after!

[Wes Grass]

Sawstop:

Same dia, .624. Arbor is about 1.3" long, and threaded 12TPI square thread about an inch long.

No removable spacer. That limits the thickness of a dado set. And probably done to keep it lined up with the brake shoe. But you'll have some flexibility there.

[Phil Thien]

If you DO decide to have an arbor fabricated, I'd sure love to hear what it costs and how it comes out.

[jon hamer]

Thanks for all of the great replies!

I think my next move is going to be to try to get a hold of an arbor from a 5/8 cabinet saw (Unisaw, for example). Once I have that, I can take all of the measurements needed to fill in the details as to the threads. I want to stay with a thread pattern that I can easily buy a nut for, and will properly support a dado stack.

I know I could sell this saw and buy another that is closer to what I'm looking for. I've decided against this because I suspect the number of production shops interested in an orphaned scoring saw (no parts or service available) is rather low, so I doubt I'd be able to get much for it. In addition, I strongly doubt I'd be able to get "more" saw than I already have with any money from a sale. I admit I've taken a shine to its crisp, front-mounted cast iron controls, too. If I make a 5/8" arbor that can support dado cutting, I'm increasing my pool of potential buyers. I'll also keep the original 20mm arbor for anyone that wants to return it to stock.

Why use a pre-hardened blank? Can't it be hardened after the machining is done or near done?

Thanks!
Jon

[george wilson]

Make sure the thread TIGHTENS the nut in the direction of rotation.

[Wes Grass]

Sure, it can be heat treated afterwards, or before finish machining. And if it needed to be really hard that'd be the only practical way to go. But using pre-hardened material saves the cost of heat treating. Roughly a $75 lot charge around here.

And in the case of 4140, it actually machines better when it's hardened a bit.

[J.R. Rutter]

Short of befriending someone at Delta/Rockwell/Invicta who can dig through files and copy a measured production drawing, duplicating the bearing side from the existing arbor is the best way to go. I would remove the arbor and take it to a machine shop and then you can spec out whatever you want for the blade side dimensions, threads, features, etc.

[John Callahan]

Jon, I'd contact Invicta USA. Invicta still makes the RT-31 afaik; it's still listed on their Brazilian website though not imported into the US. Invicta USA may be able to get what you need. Worth a try ...........

[jon hamer]

Update:
I've talked to a few machine shops - all of which say that they can make an arbor at a price I can live with. My plan is to put a 5/8 spindle onto an otherwise RT-31 arbor. My saw has a max 12” capacity, but with a 12” blade in place, I cannot lower it completely – one inch always stays above the table. The Unisaw arbor I had planned to copy the spindle from has a smaller-diameter flange (2 ½”) where the RT-31 is about 3” across. I want to know if I can still use a 12" blade on this new arbor, or if it won’t be supported well enough dampen vibration. The 12” would not get used often, only for extra-thick material – and I’ve got a bandsaw for that, anyway. The rest of the time, a 10” blade would be used. Dado capacity on the Unisaw (from manual) is 13/16 - I'd like 1". How long should my arbor be for a 1" stack? I am considering a better nut and washer, better than the cereal-box treasures that Delta sent me for top dollar… (the nut is 3/16 thick and the washer is a convex stamping, about 1/16 thick. The washer from the RT-31 weighs about 4oz, it is solid. The nut is also well made- it’s 3/8 thick and has about 6 full (1.5mm pitch) threads inside.
Anyone tried one of these:
http://www.mikestools.com/36-659-Del...able-Saws.aspx

I’ve uploaded pictures of the arbors and their components.
Thanks,
Jon Hamer

[Wes Grass]

My Felder has a 3" flange, for a 12" blade. It will also accept a 14". I don't see any reason why you can't copy the arbor and keep the 3" flange, unless there's an issue with the dado set.

[Chip Lindley]

3" arbor flange should be fine! Just check that it clears the underside of your table insert when raised to full height. For comparison, Freud blade stiffeners for a 10" saw with 5/8" arbor are 3-1/2" Dia. !