Machining a straight edge

[lucky7]

Some recent comments and youtubes had me thinking how many different ways there are to machine a part. A few years ago I machined one of Richard's HKA 24" straight edges on a 26" stroke shaper. Not the quickest machining method but good fun. I was concerned about warping the SE while holding it for machining and didn't want to have to surface grind it like Keth Rucker usually does. Mostly because I don't own a big enough grinder, but also because I like scraping a straight from a shaper finish. And the less warp, the quicker scraping goes. So to minimize warp, I took a file and scraper to flatten one of the sides to a few ppi and clamped that side to angle blocks on the shaper table. Took less than an hour but saved time later. After machining the base, I then scraped it to a few ppi and clamped the base directly to table to machine top of SE. Now with two truely parallel surfaces, it was easy to set up without warping the casting to machine the other two surfaces. Quick (for a shaper) but more importantly took very few passes while scraping for blue to come in.

Others would do it differently. That's what is so fascinating about machining work.

L7

 

[dgfoster]

Some recent comments and youtubes had me thinking how many different ways there are to machine a part. A few years ago I machined one of Richard's HKA 24" straight edges on a 26" stroke shaper. Not the quickest machining method but good fun. I was concerned about warping the SE while holding it for machining and didn't want to have to surface grind it like Keth Rucker usually does. Mostly because I don't own a big enough grinder, but also because I like scraping a straight from a shaper finish. And the less warp, the quicker scraping goes. So to minimize warp, I took a file and scraper to flatten one of the sides to a few ppi and clamped that side to angle blocks on the shaper table. Took less than an hour but saved time later. After machining the base, I then scraped it to a few ppi and clamped the base directly to table to machine top of SE. Now with two truely parallel surfaces, it was easy to set up without warping the casting to machine the other two surfaces. Quick (for a shaper) but more importantly took very few passes while scraping for blue to come in.

Others would do it differently. That's what is so fascinating about machining work.

L7

Interesting approach. How close to flat were you able to machine the surfaces?

Denis

 

[lucky7]

Denis,

Less than one thou on the base. Didn't measure the angled face. Eight scraping cycles on the base to get 3-4 ppi- good enought to clamp to shaper table.

Denis, how do you set up your 36" and 48" SE's on the HBM? Pics?

Cheers,
Stan.

 

[dgfoster]

Denis,

Less than one thou on the base. Didn't measure the angled face. Eight scraping cycles on the base to get 3-4 ppi- good enought to clamp to shaper table.

Denis, how do you set up your 36" and 48" SE's on the HBM? Pics?

Cheers,
Stan.

Good job on the 24.

I do mill the 36" on a 15 ton HBM at a local shop where I trade repair and maintaining their machines for time on the HBM. The travel on the HBM is only about 40 inches. So, i am not offering the 48 machined. It could theoretically be done in two setups, but that would be something of a hassle and it would be hard to maintain my target flatness of .0015 on the 36.

I do not have pics handy at this time, but I do have a 36 that just sold and needs to be machined. I will try to make some pics and a brief video. I do use a somewhat uncommon method of fixturing it in a way intended to minimize flexion of the casting.

Denis

 

[Richard King]

As old timers on PM told me when I started to write here years ago. I can say the same thing now. Everything has been discussed before at least 2 time before

Planing a straight edge

Machining Straight edges

Prepping a Straight Edge for Scraping

 

[dgfoster]

As old timers on PM told me when I started to write here years ago. I can say the same thing now. Everything has been discussed before at least 2 time before

Or as famously said by (well erroneously attributed to) Charles Holland Duell (April 13, 1850 – January 29, 1920) was the Commissioner of the United States Patent Office from 1898 to 1901,
"Everything that can be Invented has been Invented" 1902

So, I guess we may as well quit tryin' boys; there can be no new idears worth knowin. I love it!

Denis

 

[Richard King]

But can the new things compare to long known methods to something simple. One thing that you can read in the first Stephen Thomas thread I listed on the 3 rd paragraph. Planing a straight edge

"At some point I read a post by Richard King which described his experience owning a couple old planers. He mentioned that one planer he had owned would not plane flat, but that with the straight edge laid on it side and planing down with the toolslide, he was able to get adequate work as a starting point for scraping. I had mapped my planer when acquired, and despite a fair amount of error from flat at each end (.006" give or take) it was difficult to find error sideways."

If you machine or plane the straight-edge use the side of the cutter on a mill for finish passes because if the table sags on the ends the side of the edge stays straight on the horizontal plane versus the bottom of the cutter machines the ends of the straightedge low on the ends as the knee sags due to gravity. Same goes for a planer as he points out. top pane was out.006" and side was difficult to find an error.

If anyone would like more info from someone who is a Journeyman rebuilder, please PM me as I prefer not to get insulted in the public forum.

 

[CBlair]

Richard, that is a good point and could be useful for someone who starts to have trouble getting good results. It is also a good reason to use a horizontal spindle as it helps in the same way.

Of course a standard vertical machine in good condition is capable of achieving good results. But for those who have trouble it is a good idea to keep these lessons in mind. Thanks for bringing them back to our attention.

Charles

 

[dgfoster]

Preamble (skip this if you want.): I am currently machining one of my 18's for a PM member. The inquiry raised in post 3 above will have to wait until I am machining a 36---the next week or two. I figure it may be of interest to some for me to report on the some of the methods I have learned/developed for machining one of my 18's as its unique design (And similarly the design of the 36) calls for fixturing it in ways somewhat different than used for ordinary SE's of similar length. Both could be machined nicely on a planer too, but I don't have one at my disposal and even so it would need some attention to fixturing to avoid inducing twist or warp in the casting due to clamping pressure. No doubt there are other and perhaps better methods than what I use, but I will post what I have come up with to serve as a starting point for folks who have bought raw Feathereweight 18's and to serve as a discussion starter for those with suggestions as to how to do it better. For the 18 I am using a 1 HP Bridgeport with Accu-Rite DRO and factory table feed. Overall it is quite good condition with ways in good condition and table that reasonably, but not perfectly, flat. For the 36 I am using a Lucas HBM that came out of Boeing.

Using reasonable care, I am able to get flatness of .001 in each of the two main surfaces milled and the top rail parallel within a few tenths. That seems like an acceptable job for the intended purpose---gotta leave something for the scraping hand to do, right? ;-)

I have tried making my cuts with a 3" face mill using both a right angle head which allows the cut surface to be vertical to the bed (and in theory may be preferable) and with a conventional setup. On my mill I get similar results and use the conventional setup except for facing the ends of the casting and boring fixturing holes (which can later be used for attaching handles should the user desire. I do follow the usual precautions of allowing the casting temperature to normalize prior to making final reference surface facing cuts.

I will do my best to provide a clear description of the method I use, but if what I post needs clarification, I will do my best improve it.

Now some pics:
Obviously the first step is to clean off some of the gating and flash from the casting.

Then I setup my right angle head and align it. I have milled reference flats on the side and bottom of my head to make tramming it easier.


I use a simple little jig (orange in the photos) to locate a punch mark.



That's the limit of five images per post. Sorry, I know this is pretty basic stuff in this post. But if I don't go step-by-step, there may be questions.

Denis

 

[dgfoster]

Next a few pics and notes about the basic setup and end boring.





Once the mounting holes are in place the casting can be mounted "on a spit." I think the spherical washers are key to avoiding inducing bending stresses into the casting. Prior to using them, I had some difficulty get good flat cuts.




I don't think simply supporting the casting on each end would be rigid enough (though I have made cuts that way without difficulty) so I block it in both front and back with clamping straps to prevent unwanted rotation and, as a side benefit, resonance damping. I just snug the clamps lightly and tap with with a dead-blow until they are seated.


Getting the head of the mill accurately trammed is essential for making a flat cut. A shortcut when using the 3" facemill has been to first make a couple rough cuts with the head trammed to day-to-day standards and then use that face as a means of gaging tram. I just place the head somewhere on the cut surface and crank the knee up until it kisses the face. Then I adjust the tram until the cut is uniform both left and right. Using that method had been simpler and at least as effective as the conventional method using a DTI.

Well, that's five.

Denis

 

[dgfoster]

Here is the cut surface showing cross-hatch obtained with tramming.

I'll take a few more photos today as I finish the casting and will add in a video or two.

Denis

 

[ripperj]

Cool! Do a good job, I heard the buyer is picky



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[dgfoster]

Cool! Do a good job, I heard the buyer is picky



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No problem. Featherweights are aimed at the discerning customer! ;-)

Here is a quick an dirty look at one side of one surface chosen at random just to show that the surface is adequately flat. By rights I should get my blocks matched perfectly for the demo, but no time for that now. The right hand block is about a thou higher on this surface than the left resulting in a straight line rise as I scan to the right.

Denis

 

[dgfoster]

This morning I cut the radius where the upper prism surface intersects the top parallel rail and cut the top rail final cut. The radius serves two functions. Most importantly, it provides relief for scraping that surface. Were it not there the scraper would be scraping into blind corner—-no fun. And secondly, the round recess makes a very comfortable spot for the user!s finger tips when lifting the SE. The right-angle head makes this cut easy as the recess needs to align well with the top rail cut or else it looks wonky. So I make the two cuts in one setup.

Later I will mill a flat on the inside bottom surface of the prism and drilld tap the holes for the Precision Geier and Bluhm level vial. That is step also uses the right-angle head.

BTW, I did a better job of scanning the bottom plane of the prism taking more time to clean the surface plate and the blocks. I’ll make video later of that as I am not proud of the quick (yes) and dirty (that too) video I linked in the above post.

Denis

 

[dgfoster]

Getting setup to drill and tap Geier and Bluhm precision machinist’s vial holes after milling a bed for the vial.
Pictured below is a right angle boring and tapping device I designed and built to do this job as the overhanging top rail and prism face don’t allow access for conventional drilling and tapping.





the drill and drive pulley are held in place by the steel plate that has the two torx screws in it.


Underview of the drive pulley located in a 1/4” collet in the mill spindle.


Cutting the holes will have to wait a few hours.

Denis

 

[dgfoster]

I got back to it this afternoon and did the last steps---drilling and tapping the mount holes for the precision vial. That step always makes me a little nervous as making an error locating the holes or breaking a tap or drilling too deeply would screw up all the work to this point. Fortunately no gremlins bit me today and all went well. So the machining is done and now it is just boxing it up and sending it on its way.

A few pics:
Here is a pic of the 5-40 tap tigged into its drive pulley. The stock pulley is aluminum, but bore them out and inset and loctite in an axle that rides in the right angle boring rig and carries the tap.


Here is a junk vial holder (no vial in it) that I use to check prior to shipping to confirm that the holes are correctly located and the holder will actually fit into the SE. Seen to the right in the picture is a shop-made 5/64" hex wrench the fits under the vial holder tube and allows tightening of
the mounting screw in the back. Without the tool it is challenging to secure that screw. I wish there were 5-40 Hex-head bolts available. But I have not found any doing a casual web search of the usual suspects. So, since it would be otherwise tough for the purchaser to secure that screw, I include a wrench with the SE.


The geometry of the SE limits the depth of hole that can be safely used, so I grind off .030 from the screws and send four along with the SE.



This ois the block that holds the screws for grinding on the surface grinder.


I am always glad to have the SE fully machined as any momentary lapse along the way can result in expensive (in hours spent beginning with packing the mold to final machining) scrap.

I'll post up a few pics of the wood box crating tomorrow and then slap a label on it!

Denis

 

[dgfoster]

I did do a simple parallelism (and straightness) check of the top rail. I am surprised the BP cuts as straight as it does, frankly. That cut was made with the SE simply placed with the sole clamped to the table and a horizontal cut made with a 1.25” facemill. It looks like the rail is within .0006 or so of flat and parallel.

I will try to do a better survey of the sole, but I can't run the camera and the indicator by myself. I'll see if I can draft my wife to be cameraman tomorrow.

Denis

 

[ripperj]

Thanks for posting the machining sequence.

It’s pretty cool to see a tool being made that will end up in your shop.
I have been in need of a quality reference surface for a long time now, I really hope I can make it work this fall with the VT scraping class.

I definitely need to keep looking for a right angle head for my knee mill, I am struggling with the insane prices they get for the Cat40 ones for the VMC.

I’ll get payment out today.

Thanks again
Keith



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[dgfoster]

Don't forget that you get the 10% discount just for being a PM member. And you will get the additional 20% off on completion of your course. Thanks for your business! And best wishes for an enjoyable and educational scraping class. I'll ship just as soon as I receive the G+B vial.

Denis

 

[ripperj]

Can you check your email please, I need an address to send payment


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