Singer 7- prone to cracking ?

[Silky]

Is the Singer 7 class prone to cracking in the area circled in this pic ?

Anyone see one cracked here ? Looks like a weak area.

Thanks

Edited October 14, 2019 by Silky
spelling

[Constabulary]

if you don´t drop it it will most likely never crack. Singer 18 also looks fragile but never heard of a broke arm from just operating the machine.

[Silky]

Thanks ! It does look pretty tough.

A relative tells me of an old machine in a building. It has Singer 7-(something) on the plate ... not sure what the # is.

She says It is big and has what looks like a a vertical spindle with a toothed pulley on the head alongside the needle.

I searched for class 7's with a drill or awl but came up blank. Until I can get some pics, does this type of machine sound familiar to anyone here ?

Thank You.

[Gregg From Keystone Sewing]

Singer 7-33 has two issues that come up if you've seen enough of these machines.

The take up lever hinge screw if it becomes loose, can break the casting or threads.  This is why Consew and Seiko have a removable take up lever bracket if this happens.  On a Singer, it's a much bigger deal.

Now, when the Singer 7-33 breaks at the beak, it's just about done.  I've seen brazing that has held up over time on some repairs that come in that I guess hold up, but it's not a machine I would buy to rebuild.

Once in a while someone will over tighten the race saddle that has a single clamp screw through the casting of the bed.  This is a problem too, but only if someone decides to over tighten this.     

Some of these were from the 1930s and offered as a extra heavy duty canvas machine with a maximum presser foot lift of 9/16 inch.  Most are doing much more than that now with very heavy presser foot pressure.  

[Silky]

4 hours ago, Gregg From Keystone Sewing said:

 Now, when the Singer 7-33 breaks at the beak, it's just about done.  

Hi Gregg. Is the "beak" area break you mention referring to the circled place on my attached pic ? Never heard beak before.

I guess that end of the machine does somewhat resemble a birds head with a beak down towards the needle.

Thanks for the tips.

[jimi]

 From that picture looks like that pressure bar is bending a lot!!!

[DonInReno]

Repairing a simple crack in cast iron with brazing is not always easy - and not every welder or machinist will even try.   Sewing machines are covered in an oil film and any crack will have to be ground out and the surrounding area cleaned well.  Preheating the area often shows additional cracks as oil works to the surface - those have to be ground out before continuing. 

The faster the cast iron cools the more likely it is to crack - so much of the machine will have paint damage from good preheating and slow cooling. 

Brazing shrinks as it cools, and the repaired area is attached on both sides of the break to the cast area below so that puts stress on the entire area - the repair may crack, or new cracks may appear.  I have a cast iron spoke on a handwheel in a similar arrangement that has been repaired at least three times and needs a fourth.

Sometimes everything looks to go smoothly and there is just a problem area that refuses to cooperate and the repair has to be ground out and repeated.

Ive heard others with much more experience say they avoid brazing altogether and weld cracks with nickel welding rod - there’s a lot of wisdom in that.

Another challenge has to do with bent areas containing micro cracks - cast iron of the type used in sewing machines can bend a bit before cracking - or small cracks exist around the bend that are small enough to not show through the paint.  If small cracks aren’t causing problems you may not want to mess with them.

 

 

[Gunnarsson]

8 hours ago, DonInReno said:

 I have a cast iron spoke on a handwheel in a similar arrangement that has been repaired at least three times and needs a fourth.

One method to deal with cracks in spoked cast iron wheels (and many other places) is to preheat the spokes next to the broken one, or similar places. This makes the surrounding structure cool down and shrink along with the repair, avoiding causing tension and new cracks. I've got a few old O/A welding handbooks with pictures showing the basics, if anyone is interested.
Another method is to preheat the entire piece. 

Anyway, cracks on a sewing machine body is hard to deal with, you want to preheat it all but that would force you to disassemble it completely, and repaint. A bigger job than most people want to put into it.

[chrisash]

Once found a story about Benzona for repairs of cracks in cast iron, think it was a epoxy blanket or similar, might be worth investigating

[Silky]

Well it turns out that the machine wasn't cracked, it was just a scratch in the paint. 

Thanks for the info on welding/brazing, much appreciated.

I have welded (and brazed) many cast Iron pieces over the years and have been quite successful at it. The preheating is a good idea .. where practical. For my best results on delicate, as well as larger items that are impracticable to preheat , I never let the base part get very (relatively) hot. Stick weld with machinable nickel rod one small puddle at a time, quickly peening with a small radiussed pointed chipping hammer until the heat dissipates into the neighboring casting while cooling to where you can just barely keep your bare hand on it briefly without getting burned. Then repeat  until the ground out prep area is filled. This stress relieves the filler material as you go and tends to relieve the stress in the parent material as well  It takes MUCH patience but usually comes out quite well. Depending on the quality of the casting, and inclusions, the Ni rod will not flow well with the base material. In this case, I run a light pass of Ferroweld which acts sort of like a primer and improves the fusion of the Ni to the casting, then finish filling with the Ni. The main attribute of the NI is that it is malleable and machinable, where the Ferroweld is too hard to machine and does not stress relieve by peening like the NI and it is more prone to cracking as it cools and contracts.

The other main problem is that whatever you do, if the piece you're welding has a precision bearing journal at each end, or other critical feature, there will be some deformation affecting the alignment. Sometimes a little bit is OK, other times align boring/honing or re-machining is necessary to restore functionality.

Thanks folks.

 

[DonInReno]

12 hours ago, Gunnarsson said:

One method to deal with cracks in spoked cast iron wheels (and many other places) is to preheat the spokes next to the broken one, or similar places. This makes the surrounding structure cool down and shrink along with the repair, avoiding causing tension and new cracks. 

I agree preheating is very important.  I like to evenly heat the entire piece to 1000 degrees F, do the repair, and cover with multiple layers of fiberglass welding blankets to slow down cooling.  

[Silky]

12 hours ago, DonInReno said:

I agree preheating is very important.  I like to evenly heat the entire piece to 1000 degrees F, do the repair, and cover with multiple layers of fiberglass welding blankets to slow down cooling.  

This works well for smaller parts when practical, especially with something like a spoked wheel.  Submerging the part in a tub of dry wood ashes is also an excellent medium to slow the cooling.

[councilman24]

I've never heard of one cracking. See post on 7-33 needles for very good manuals.