View Full Version : Cutting teeth on a long rack
I have an old Craftsman table saw that was made when Craftsman still made respectable machines. I am planning on extending the table to allow 24" ripping capability. The cast iron table is already drilled to accept an extension, and I plan on welding my own extension and bolting it to the existing table. The fence on said saw has a rack and gear setup to finely adjust the fence. I would really like to make a longer rack to coincide with the table extension. I haven't made any measurements on the teeth on the rack, but they are pretty fine. Does anyone have any suggestions on making a longer rack? I have a Grizzly M/D at my disposal, but can't figure a way to do it. Maybe some sort of ttapered endmill? I've never seen such a creature, but that don't mean it don't exist! http://bbs.homeshopmachinist.net//biggrin.gif
Thanks in advance.
02-14-2005, 11:43 AM
You could grind a profile cutter similiar to a fly cutter that matches the tooth profile of the existing rack. Another choice would be to buy a gear hob of the proper pitch.
02-14-2005, 11:44 AM
They do make tapered cutter but the problem is the size of the tip.
Smallest I have found in 20 degree is 1/8" at the tip which is a biggish tooth.
There are no off the shelf 14.5 degree cutters but there are 15 degree ones.
Again it's the tip size, 3/32 in this case.
I dare say you can get one custon ground but that could be costly.
What about a length of of the shelf rack ?
He has a mill drill so is limited to using vertical tools.
Side cutting tools like fly cutters will only do a short length of rack placed vertical.
You can't hob racks with a normal gear hobber, they can be hobbed on a special hobbing machine with rack hobs, rare and very expensive.
[This message has been edited by John Stevenson (edited 02-14-2005).]
02-14-2005, 01:14 PM
I replaced mine with a Bessmier(sp) fence about fifteen years ago. I love it over the old Craftsman one. I may even have the old one around, I'll look.
02-14-2005, 01:23 PM
Don't know if you've ever thought about replacing the existing fence with a Biesemeyer Fence. I did that on my old Craftsman saw. Now able to rip 30" right & 12" left. Here's one that just sold on eBay for $167.00
Biesemeyer used to have a "scratch & dent" area on their website, but I couldn't locate that today. Their fence is awesome, dead accurate every time. And you'll never again have to use a tape measure to set the fence.
02-14-2005, 02:21 PM
Funny how this topic has come up....
I've just set up to cut a rack for the T&C grinder I'm making.It's only 9" long but still too big to get in a vertical mill.I'm doing it in a vice on the vertical slide mounted on the lathe cross slide.
The cutter is on a long arbor,one end in the chuck and a centre support at the other end.I made the arbor to go between centres,but fastening it in the chuck seems a bit more rigid.
Hope to start cutting it tomorrow,will post a pic if it works out.
It's a good job that J.S. is only a phone call away to put me right,thanks John.
02-14-2005, 03:12 PM
I've cut racks with a slitting saw before in emergencies. A fly cutter may work too.
Have to make the cuts on one side of the teeth, reset the head and cut the other sides.
It's tedious, but gets it done.
Need a right angle head, to work horizontal, or angle plate to set the blank vertical.
That depends whether your machine sets for angular cuts.
You may be able to do this on a table saw in aluminum, or brass, with some tooth spacing fixture.
02-14-2005, 08:42 PM
I would make a homebrew Biesmyer fence,anybody with a chunk of square tube and basic tools can do it.
02-14-2005, 09:02 PM
There are plans to build one in a book I have. I'll copy & fax to you if you want. Looks like about twenty hours labor and $50 - $100 in material. Bought mine used and it still took four hours to mount, level, align, drill & tap.
Best thing about the Biesemeyer is that you're able to adjust parallelism of fence to blade. Jim Forrest (Forrest Mfg) recommends that the back end of the fence be adjusted 0.010" - 0.015" farther away from the blade than the front. Easy to do with Biesemeyer's adjustment feature.
02-15-2005, 02:06 PM
<font face="Verdana, Arial" size="2">Originally posted by precisionworks:
....Jim Forrest (Forrest Mfg) recommends that the back end of the fence be adjusted 0.010" - 0.015" farther away from the blade than the front. Easy to do with Biesemeyer's adjustment feature.</font>
What's the reasoning behind that?
02-15-2005, 02:12 PM
I've cut racks. No biggie, just repetitive. If you're smart you don't cut them.
Your best bet is to find a stock rack that has the right Dp and Pa and modify it to suit your application. Best $30 you'll ever spend.
02-15-2005, 02:15 PM
I would be very interested in the outcome of your cutting arbor and look forward to your pictures and results. If the system is rigid enough it should accomplish the rack Arbo needs.
02-15-2005, 03:24 PM
At the moment it stands at 18 teeth cut and only 41 left to do.I'll post some pics tomorrow hopefully.
The arbor is a length of 1" bar with the cutter holding boss Loctited on.
The rack is 3/8 wide and I'm using a 20DP cutter.I've got a bit quicker and a little bit more confident since the first four teeth,but it's quite a boring and repetitive job,as Forrest said.
Bit of a bad day really,had to have the cat put to sleep this morning,he was diagnosed with leukemia,no cure.
02-15-2005, 04:06 PM
Sorry about the cat. We have had several cats die from cat leukemia even though they were vaccinated. One cat, though being very sick - pulled through and has been okay ever since. For those who don’t know about it, here is a link that describes it.
Glad to hear that the method you devised to cut the rack is working. I’ll probably have more questions for you – so be forewarned! http://bbs.homeshopmachinist.net//wink.gif
[This message has been edited by Mike Burdick (edited 02-15-2005).]
02-15-2005, 07:56 PM
Forrest Mfg. suggests the additional gap so that your workpiece isn't trapped between the blade & the fence, causing a kickback.
02-15-2005, 08:24 PM
Ted mentioned to get a hob of the proper pitch.
It was my understanding that a hob was basically a screw thread that had the form of a rack on it's diameter, it then turns in at a speed relative to the gear blank (ie: an 8 tooth gear, cutter turns eight times, hob turns once).
Is this correct? If so, I do not understand how a hob could cut a rack.
02-15-2005, 08:56 PM
It can't, see post #3.
There are rack hobs made, these are like a gear hob but consist of concentric grooves instaed of a helical groove.
In essence thay are just a bank of single cutters machined as one.
These will cut the number of rack teeth equal to the number of cutters making the hob up.
So if you have a 10 groove rack hob you cut ten teeth, move along 11 teeth and take another bite.
Specialised cutter and specialised machine to run it.
There is an attachment that fits horizontal mills to allow racks to be cut in long lengths.
Basically it's a stubby right angle drive that allows the cutter to drop below the attachment casting, a problem that most machines have.
Using a simple gear setup for indexing you can cut one tooth and move along.
Even a Bridgeport is limited on doing a long rack because if you try to replicate this setup by spinning the head so it's parallel to the bed the head / quill gets in the way of the rack.
02-15-2005, 09:47 PM
All you who have shapers stop laughing! This is too easy on a shaper,grind astandard acme threading tool that matches the pitch of your rack,set the down feed to 0 touch off with the tool ,feed to depth ,move over the pitch of your rack and do it again.No problem standard or metric.
02-16-2005, 01:23 AM
Of course, a mill can be used as a shaper, as well. Grind the proper form on a suitable piece, chuck it in the mill, and use the downfeed to 'broach' the teeth. This will get tiring as well, but at least you can get the job done without a right angle attachment. You can do a really long rack if you first cut several teeth, then make up a fixed tooth on the table that fits into the cut teeth on the rack. When the table limit is reached, crank it back and reposition the rack, using this fixed tooth to align the rack with.
Or just pick up a piece of threaded rod of the right pitch, and use that as your rack.
02-16-2005, 09:31 AM
I have pieces 'n' parts from late 70s saw. The rack seems to be 10 tpi, but my 2.5mm gauge fits better, and about .060 deep. If interested, e-mail me and we can work something out.
02-16-2005, 10:04 AM
heres my own table extension with home made beisemeyer overhead guard and fence hope you like them. Alistair
02-16-2005, 10:52 AM
Mr. Hosie, Exactly how much time do you spend cleaning? I have NEVER seen a table saw that has ever actually cut anything ever that clean. There isn't even a speck of sawdust on the floor. When my shop is clean it isn't nearly *that* clean. Very nice.
02-16-2005, 11:52 AM
James it isn't always that clean these photo's were taken after I installed the new flooring.I usually get help to keep it clean from my wife but rest assured it is not always that clean http://bbs.homeshopmachinist.net//biggrin.gifAlistair
02-16-2005, 12:15 PM
Nice job on the guard/vacuum pickup. Even with a sealed base & 2HP collector, lots of sawdust escapes the guard.