Making a Rack, how to secure to table?

The shaper has auto-downfeed, I think I'm taking .003 per stroke. While I agree that the deeper the bit goes the more metal is removed, I see videos of similar shapers taking 1/2" cuts 3/8" deep per stroke. I am a novice on this machine, I thought I was well below the maximum cut per stroke.
I am no longer trying to use a vise for this job.

I agree the shaper can take some serious cuts. Those are usually taking a cut on one side of the tool, and the tool is ground to cut only from one side. Is your tool ground to take the cut from both sides, and the bottom? A neutral rake on any sides of the cut will take a lot more force to cut, and therefore will require that much more clamping on the table.

I would look into designing a fence to take the force from the rack, and prevent it from bending. The stronger the fence, the less pressure you will need on the clamps holding the rack.
 
Superburban,

I used a 5 degree rake off the bottom and sides to give relief. I tried to make it the same way as a keyway cutter. The bit is honed on both sides and the bottom. I am using a 3/4" piece of NOS (REX or Circle) tool bit for rigidity.
 
I made 3 racks for a CNC plasma table a few years ago. A lot smaller than your working with but the principals can be scaled. I needed the tooth placement to be as accurate as possible in order for the cnc to be accurate. I used the vertical mill to drill and ream holes for dowel pins down the length of the material at 6 or 8 inch spacing. Then made 3/4 x 2 plates with reamed holes to accept the same dowel pins. The plates bolted to the shaper table.

IMG_0835.jpg


Made a solid mount, your angle iron method would be similar but I'd expect the angle to flex. With the dowel pins through the two plates it was held down quite solid.
I added a DRO to the machine to space the teeth. After cutting a section i could index the material over on the dowels and reset the DRO the known distance I moved the material. Only the rear plate was removed to index the stock, the front plate held my reference.
I cut the three of them at once, in the end I could rotate one 180 degrees and the teeth meshed end to end so the indexing worked.

As Superburban suggested try rotating the cutter head as you would threading so your only cutting on one side. Worked for me.

IMG_0890.jpg


If I remember I was taking 10 or 12 thou cuts at the beginning then 1 or 2 thou cuts at the full depth. Didn't have the luxury of power down feed, still don't on my 18 inch Peerless.
Hope that gives you some ideas.

Greg
 
I made 3 racks for a CNC plasma table a few years ago. A lot smaller than your working with but the principals can be scaled. I needed the tooth placement to be as accurate as possible in order for the cnc to be accurate. I used the vertical mill to drill and ream holes for dowel pins down the length of the material at 6 or 8 inch spacing. Then made 3/4 x 2 plates with reamed holes to accept the same dowel pins. The plates bolted to the shaper table.

View attachment 257117

Made a solid mount, your angle iron method would be similar but I'd expect the angle to flex. With the dowel pins through the two plates it was held down quite solid.
I added a DRO to the machine to space the teeth. After cutting a section i could index the material over on the dowels and reset the DRO the known distance I moved the material. Only the rear plate was removed to index the stock, the front plate held my reference.
I cut the three of them at once, in the end I could rotate one 180 degrees and the teeth meshed end to end so the indexing worked.

As Superburban suggested try rotating the cutter head as you would threading so your only cutting on one side. Worked for me.

View attachment 257118

If I remember I was taking 10 or 12 thou cuts at the beginning then 1 or 2 thou cuts at the full depth. Didn't have the luxury of power down feed, still don't on my 18 inch Peerless.
Hope that gives you some ideas.

Greg
Greg,
Thank you for the photos, they are a real help; I like your idea better than using the angle iron. In your last photo, I see that the clapper box is angled but it looks like the tool bit is set perpendicular to the work, effectively cutting on both sides at once. What am I missing?
I'd like more information on your DRO for the shaper, can I impose upon you to ask you to either post info here or send me a message?

thanks,

Mike
 
Yes the clapper is angled to match the pressure angle of the rack.The tool still needs to be perpendicular to the work, same as threading but it advances along the one side of the tooth, same as swinging the compound on the lathe.
I used I-Guaging DRO's on the Logan, worked great, was surpsided at the accuracy. Only problem with them is setting to a position, you can't enter the dimension, only zero them. I left them on it when I sold the shaper.
Wanted to put a DRO on the Peerless but the clapper retracts way into the housing on the back stroke. Wasn't enough room for a glass scale. Upgraded the mill to a 3 axis glass scale kit and transferred the old Shooting Star 2 axis I've had on it for 15 or more years. It used a small rack with an optical encoder to measure the movement. Quite compact, still a tight fit on the clapper though. The rack is round, the teeth are on the back side here.
IMG_3898.jpg


The cross feed was fairly easy to mount to. Funny they didn't cast nice mounts in these old machines for future DRO's
IMG_3899.jpg


Pretty simple readout. Reads to 1/2 thou

IMG_3900.jpg


Hope that helps Mike

Greg
 
I think you have most of the bases covered, except for the the main question you asked. Sorry for side tracking so much. Greg's (F350CA) first two pics tell it all. With the blocks like that, you should be good to go to take the large cuts. remember, you need something like the block Greg has to keep the work piece from moving under the heavy cuts. After that, the actual hold down of the piece won't require as much pressure. I have done similar with using the big hold down clamps as a back stop, but will take Greg's idea, and make backstop, with the holes to make it easy to attach to the table.
 
This is the exact method I used to cut the gear to mate with the rack. The length of the rack prohibits me from using the horizontal mill to cut the center out of each tooth. This is hot rolled steel, I am hoping not to have too much curling of the blank.
You can do long racks on a horizontal mill if you have the rack milling attachment, which has a cutter arbor at 90 degrees to the spindle axis; spacing is done with a change gear device with a one rev. detent; the sections of rack are held in a special vise, much like the one shown made out of rectangular bars, but is self contained. Also, rack can be made in sections, as many longer lathe carriage racks are.
 
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